regular circle. They are quite as much inclined, and their hooks are stronger, and more arched at the point. The radiating striæ are also more visible.

In front of this double row of escutcheons and as if forming their immediate continuation on the inner side of the pectoral fins, and in front of them, we observe a subtriangular bone, the anterior side of which is concave, bordering the branchial opening beneath. These two bones are contiguous on their anterior angle, and form by their reunion a convex curved line along the sides of the mouth, to which the branchiostegal membrane is attached. A prominent carina, but unprovided with hooks, extends along the median line from the posterior angle. A single wrinkle indicates on the middle of the anterior angle the rudiment of a carina. The striæ radiate from those two centres. The bone of the anterior part of the pectorals and upon which these fins articulate, is small and hidden under the skin.

An odd elliptical escutcheon with regular outlines is situated in the middle of the space between the anus and the anal fin. It has a slight median carina, over which projects an elliptical hook. A rudiment of an escutcheon leans towards the anterior margin of the anal.

The anus opens in a small depression immediately behind the ventrals, at a distance of about two-thirds of an inch from their posterior margin, and one inch and three-sixteenths from the anterior margin of the anal. It is small and surrounded by a cutaneous membrane, bilobed on the posterior side.

The skin over the whole space which the escutcheons do not cover is rough to the touch. Small tubercles with acute points cover uniformly its surface, being every where of equal size and at an equal distance from each other. On the terminal arch of the tail they become lengthened and flattened, and invest the whole space like scales.

The fins are generally small; the dorsal, broader than it is high, is triangular with the upper margin concave. It is composed exclusively of soft rays, with the exception of a fulcrum situated on its anterior margin. The rays are articulated and subdivided only at their extremity.

The upper lobe of the caudal is formed of small bony rays, short

and strongly inclined backwards, not reaching the extremity of the fin. The rays of the lower lobe do not differ from those of the dorsal. They bifurcate like these latter, but at the extremity only. The posterior margin of this lobe is notched, in the form of a crescent and elongated in its upper part, along the arch of the tail. The notch is not deep in the lower part.

The anal is opposite to the dorsal, beyond which it extends backwards. It is narrow, elongated, almost twice as high as it is broad. The inner and outer margins are almost straight, the terminal oblique margin slightly curved. The rays are slender, bifurcated at their extremity only.

The ventrals, similar in their form to the anal, are situated at the posterior third of the body. Their structure has nothing that distinguishes them from the anal.

The pectorals are as in the A. laevis the largest of all the fins. Their form is lengthened, the terminal margin is obliquely rounded, and passes to the inner margin by an arch. The anterior and outer margin bears a spinous ray, bent beyond its insertion, and curving inwards a little before the point. It does not reach the extremity of the fin. It is flattened in the horizontal diameter of the fin; its basis is three-sixteenths of an inch broad and terminates in an obtuse point, in the margin of the fin. The surface is striated longitudinally on both surfaces, alternating with small furrows and wrinkles. The soft rays are as in the other fins.

The general color is of a yellowish brown on the upper half of the body, the yellow growing purer on the sides and beneath the belly. A large spot of an intense black, and an elongated quadrangular form occupies, on the middle of the back, the space between the dorsal and lateral series of shields. A second pair of large spots of the same color occupies the same position on the sides of the dorsal fin, on which they even encroach a little. Other small spots are distributed over the sides of the fish from the opercular apparatus (itself included) to the tail and the fins, giving thus to the whole fish a dotted appearance.

P. 1, 43-35; V. 26-28; D. 36; A. 25-28. C. lower lobe more than sixty.

The only specimen of this species which is in my possession was found at Michipicotin on the north-east shore of Lake Superior. Though this species is very similar in its general characters to the Acipenser maculosus Lesueur, from the Ohio, we have not, however, been able to identify it. The description which this author gives of his species is so vague that he does not even tell us the form of the fins. The formula of their rays is far from corresponding with that of our species. Nor is the abdominal series of plates the same; those of the sides and back seem to resemble it more closely. The snout is also more slender; but had not Lesueur mentioned that the species which he saw is of small size, we might have supposed that our specimen was the young, which have generally the snout more pointed than full-grown specimens.

ACIPENSER RHYNCHEUS, Agass.

This species is very similar to the preceding; it differs from it only in a few characters which we shall here enumerate briefly. The body is more slender and diminishes less abruptly towards the caudal region. The curve of the back is more elliptical; slightly concave at a small distance behind the head, where the third escutcheon is sensibly smaller. The head is contained about four times in the whole length. The face, from the anterior margin of the branchial cavity, forms the fifth part of the length of the trunk, and the snout from the nostrils is in the proportions of one to five. The whole length of the fish is nearly twentythree inches. The head is slender, elongated, proportionally narrow; its upper surface is very sloping, forming a line feebly broken. at the level of the nostrils. A sinus quite deep, widened on both sides, extends along the median line of the skull; narrow at the top, it widens before it disappears upon the snout. The frontal and parietal bones are carinated in their middle. The snout is pointed, but truncated. It is completely covered with small plates which pass before the nostrils and go to join again the bone which terminates the lower and posterior angle of the face. The nostrils open in a bare space which is situated under

the eye. Their form and direction are not quite the same as in the preceding species.

The shields of the dorsal series are sixteen in number, cordiform as in the preceding species, but longer than they are broad, approaching however more to a circle. The right and left margins are equally denticulated. An odd plate of medium size is situated behind the dorsal, and behind this latter a pair of much smaller plates fill up the remainder of the space to the anterior margin of the caudal. Both are carinated and provided with a hook.

The lateral series consists of thirty-five pairs of plates, elongated, narrow, irregularly triangular, the most acute point directed upwards, much resembling those of the preceding species.

The abdominal series has from eight to nine plates, generally more irregular, more strongly denticulated, with a strong carina and prominent hook.

The articular bone of the pectoral fin is stronger and more widened. The pectoral fins themselves are longer and more rounded on their posterior margin. The anal is also more narrow. The other fins resemble each other excepting the caudal, which seems to be less furcated. We have not been able to make a fuller comparison of the two species, having had only a dried specimen of the latter in our possession. The following formula of the rays is only an approximation, as the fins are somewhat defective.

P. I, 32 or 33; V. 26; D. 34; A. 25. C. lower lobe one hundred and more.

Very distinct fulcra exist along the anterior margin of all the fins, with the exception of the pectorals.

Habitat, Sault St. Mary.

ACIPENSER RUPERTIANUS, Richardson.

This species, which we did not find in our excursion, is mentioned here only incidentally, for comparison with those which we have described. Richardson has figured and described it in his Fauna Boreali-Americana. Our comparisons have been made upon a skin from Sault St. Mary, for which I am indebted to Mr. McLeod.

Its head is thicker than it is long, forming one-seventh of the whole length, which is twenty inches; the snout is covered with distinct small plates upon its surface, though it is also granulated. The frontal sinus is broader than deep, and extends over that part of the snout which is contiguous to the skull. The dorsal plates, twelve or thirteen in number, are elliptical; the lateral series number twentyfive or twenty-seven, and resemble somewhat those of the preceding species. The abdominal series have eight or nine plates, longer than broad, whilst the contrary is the case in the A. rhynchæus, from the Sault St. Mary. Their circumference is also less. The fins which we have been able to compare show but slight differences in the two species.

SILURIDE.

Whenever we are induced to consider organized beings in their connection rather than by themselves, we perceive at once differences between them, which throw more light upon the laws that regulate their structure, than the most minute investigation of isolated facts. The Siluridæ are fishes which it is difficult to combine with any other group, unless by far-fetched considerations, and afford a striking example of the importance of general considerations in the special study of zoology.

Speaking of the sturgeons above, I have already mentioned their affinity to the Goniodonts. It is now a matter of great importance to examine upon what this relation rests, for the systematic position. assigned to that family is also decisive for the Siluridæ, which are very closely allied with the Goniodonts. Indeed, Goniodonts and Siluridae may be united into one family with almost as much propriety as they can be separated, and wherever one of these groups is placed, in a general classification of fishes, the other must follow. That sturgeons belong to the order of Ganoids is now fully ascertained; but whether the affinity of Goniodonts and sturgeons is sufficient to connect the Siluridae, or whether Siluridae and Goniodonts are to continue in some connection or other with the many families of Abdominales, with which they have hitherto been combined, remains to be seen. That the position of the ventrals is not sufficient