me by Dr. Buckland, when he tried to solve the enigma in reference to Stonesfield :-"The corpses," he said, " of drowned animals, when they float in a river, distended by gases during putrefaction, have often their lower jaw hanging loose, and sometimes it has dropped off. The rest of the body may then be drifted elsewhere, and sometimes may be swallowed entire by a predaceous reptile or fish, such as an icthyosaur or a shark."

"We may also suppose that when fish or other aquatic animals attack a decaying carcass, whether it be floating or has sunk to the bottom, they will first devour those parts that are covered with flesh. A lower jaw, consisting of little else than bones and teeth, will be neglected; and becoming detached, may be drifted away by a current of moderate velocity, and buried apart from the other bones in sand or mud."

There is much probability in the last explanation. Cats generally refuse to eat the heads of rats, the skulls of which may often for this reason be seen lying detached in places frequented by them; and in the castings of owls, we often find the lower jaws of mice and squirrels, that have escaped fracture and digestion better than the other bones. Small predaceous mammals or reptiles, perhaps even birds of similar habits, may have left these jaw-bones on the shores of the Purbeck lakes or estuaries, or of the rivers which flowed into them.

Το pass from animals to plants, we are informed that a specimen of one of those flower-like fossils rarely found in coal measures, and hitherto of uncertain nature, though supposed by Dr. Lindley and others to be flowers, has been recognized by Mr. Bunbury and Dr. Hooker as actually a spike of blossoms, resembling those of the family Bromeliacea, to which the Pine-apple belongs; but it is not this particular genus that the fossil resembles. It is something to have a flower handed down to us from the carboniferous period. We can now add to our picture of the coal swamps a few bright flowers, to relieve the general sombre green of ferns and pines; and are even at liberty to hope that we may discover a butterfly that flitted amongst these ancient

blossoms.

Silurian geology contributes its quota of new matter, in the views of M. Barrande respecting "Colonies" of fossils, or in other words, alternations of beds, containing the fossils of a former and later period, at the confines of the range of the new forms, where they were gradually gaining on the older, but where in the

The

progress of the struggle, they were in turn displaced. changes in the occupancy of a given area in the sea bottom, must often have been of this character; and where the facts can be ascertained, they form good illustrations of the slow and sometimes interrupted manner in which new faunas, spreading from their centres of creation, have extended themselves ovor the earth.

M. Barrande regards the oldest or "Primordial" fauna of Bohemia as equivalent to the English "Cambrian" and to our oldest "Silurian" beds in America. Murchison, we rather think, will claim them as the lower members of his kingdom of "Siluria."

J. W. D.

ARTICLE XXII.-Description of some of the Fresh-water Gasteropoda, inhabiting the Lakes and Rivers of Canada.

In the following article we have transcribed from several works descriptions of nearly all the mollusca of the family LIMNEADÆ that are to be found in the fresh waters of Canada. Their shells are more or less abundant along the shores of all the lakes, ponds, or rivers of the country, and also constitute those valuable deposites known as shell marl. One of these beds of marl may be seen in the suburbs of the City of Montreal, where it has been laid open in the ditches crossing the Lachine Railway. Seven or eight of the species hereinafter described may be procured at that locality. In the ponds at the quarries east of the city, some of the Limneæ and Physæ are also plentiful. We have not seen the large species, L. Stagnalis, in this vicinity; but near the City of Ottawa, it is common in the Rideau river and canal. The figures given below are copied from an English work, but they represent. our species very nearly. A few days since we showed some of the Canadian specimens to a naturalist from Britain, then on a visit here, and he said they were scarcely to be distinguished from those common in the ponds and ditches in England. Ours is not quite so much angulated upon the upper part of the whorl.

* Since the above was written we have found that a second edition of the supplement has appeared, containing other new facts among which is the discovery of mammals in the secondary rocks of America.

GENUS LIMNEA, LAM.

Shell thin, oblong or turreted, last whorl large; aperture large, rounded before, narrowed and acute behind, outer lip sharp, inner lip forming a fold on the pillar, and usually spreading over it. Animal with short, triangular tentacula.

Our shell is about two inches long, the aperture being nearly one-half of the total length. It consists of five or six whorls, of which the four uppermost are slender and tapering to an acute point. The body of the whorl is as large as represented in the figures. There is a conspicuous fold on the inner lip.

This is by far the largest Limnea known in Canada, and is easily recognized by its superior size alone. *

LIMNE'A COLUMELLA.-(Say.)

Shell ovate, ventricose, extremely thin and fragile, transparent, of a pale-greenish or yellowish color, the apex acutely pointed; whorls four, of which the last is much inflated, and composes nearly the whole

shell; the upper ones are very small, form

ing an acute apex; surface with conspicuous and nearly regular lines of growth, minutely waved by revolving lines, some of which are distinctly elevated; suture slightly impressed; aperture large, four fifths the length of the shell, generally somewhat dilated; lip very sharp, ending with a small curve behind; on the left margin the edge is slightly turned over a minute umbilicus, and forms a considerable fold; a thin, closely adhering enamel stretches across from it to the angle of the aperture; the inner lip is so arched as to display a considerable portion of the interior of the shell. Length inch, breadth inch, divergence 68°; of another specimen, length 13 inch, breadth inch, divergence 56o. Inhabits stagnant pools and miry places, and is common. It is found at maturity very early in the spring.

The animal is large, semi-transparent, of a dusky or light-drab color, dotted with silvery white. It is very sluggish in its motions. The head above is slightly tinted with lilac.

This very brittle shell has rather the aspect of Succi'NEA, than of LIMNEVA. It varies a good deal in form, being in some specimens rather slender, and in others broad and distended. The aperture is usually somewhat dilated, especially at its broadly-rounded base; but occasionally the outer lip is pressed inwards. The surface is shining, and delicately corrugated by revolving lines. Var. CHALY BEA. Fig. 145.

The spire is more pointed, its divergence being only 500; the aperture is more expanded, and the fold on the inner lip more obvious. It is thin, but not very brittle, ringing like hard-burnt crockery. The last whorl is particularly detached from the preceding one, so as to form a thread-like channel at the suture. The enamel rests loosely against the shell, and is wrinkled. The exterior is covered by a bluish-black pigment, not easily removed, and the interior has a steel-blue or black-lead color.

This shell, which I found two years in succession in a muddy

pool in Cambridge, I thought was sufficiently distinct to be regarded as a new species; and I accordingly gave its characters under the name of Limna'a chalybea, in Silliman's journal, xxxiii. 196. But as it has not been found in any other place, I am now disposed to regard it as a strongly marked local variety of L. columella. It is very possibly such a shell to which Mr. Say alludes in the "Journal of the Academy of Natural Sciences," ii. 167, as “L. columella, var. a. small, black, from Cold Water Creek, Missouri." LIMNEA MACROSTOMA.--(Say.)

Shell fragile, pellucid, light horn-colored, ovate-conical; last whorl very large, moderately inflated, surmounted by three very small, oblique ones, forming an acute apex; surface shining, marked by fine lines of growth, which are crossed and rendered flexuous by numerous revolving lines, faintly visible without a magnifier; suture distinct, the whorls approaching it by a gradual slope; aperture ovate, very ample, four-fifths the length of the shell, aud, when mature, broadly expanded; outer lip very sharp and thin, broadly rounded in front, and, maintaining its sharp edge, it rises and disappears within the shell: pillar so broadly arched as to allow a view of much of the interior of the spire; a minute umbilicus is formed by a reflected scale of enamel; in mature shells a glazing of enamel is found upon the preceding whorl as it encroaches upon the aperture. Length 1 inch, breadth 7 inch, divergence 730.

This shell is closely allied to L. columélla, and in an immature state is not easily distinguished from it; but that shell is much more elongated, and regularly tapering, the divergence of the spire being not more than 60o. Such specimens Professor Adams described as his L. acuminata. But at maturity the shell is very distinctly characterized by its widely spreading outer lip, which gives great expansion to the aperture. Mr. Say received it from the rice-fields of Carolina. It is the analogue of the L. ovatus, of Europe.

LIMNE A DESIDIOSA.-(Say.)

Shell ovate, thin and fragile, the spire elongated and turreted; color a pale, dirty yellowishgreen; whorls five, very convex, and for the most part suddenly contracted above, so as to present a

conspicuous shoulder; the two or three uppermost whorls are