Chap. G. 



INVERTEBRAL ANIMALS OF VERMONT. 



155 



FllESH WATER AND LA.N'D SHELLS. 



lutions of ihe spire in a pkiiiu, and fu!>sequeiiily 

 visible o;i boiii sides ; ap'.-rti'rc liniated by tin^ in- 

 trusion of ihe p'-nuit uhorl ; operculum none ; 

 animal long, rolled ii|i like liio shell ; )iead saddle- 

 shaped; tenlacles long, corjlraclile, wiih the eyes 

 at their inner base. 



Planorbis Jrnitn.;^ I', cnrjiidcntus, and 

 P. trivolvis, of Sav, are undoubtedly va- 

 rieties of one species, to all of which the 

 following description Vvill ap])ly. 



Descriptio.v. — Shell brown, sometimes 

 greenish, coarselystriate across the whorls, 

 of which there are ibur and a half; inner 

 whorls sharply carinate on the left side ; 

 suture very deep, except between the in- 

 ner whorls of the left side, where it is not 

 depressed below the carina ; inclination 

 of the shell to the left from a perpendicu- 

 lar 15'' to 20" ; a]jerture extending bej'ond 

 the plane of the left side, sometimes be- 

 yond that of the right side, narrowing 

 from the right to the left, with about three 

 quarters of the height of the penult whorl 

 moderately intruding. Greatest breadth 

 1.1 inch ; least breadth 0.36 inch ; height 

 of aperture 0.58 inch. 



Remarks. — Sometimes the carination 

 of tlie left side extends through all the 

 whorls. The extension of the aperture 

 on the right side is of a very variable 

 character, especially at different ages, 

 and in some localities the growth is very 

 exuberant. A remarkable example of the 

 latter case occurred in Otter Creek, just 

 below the falls in Middlebury, where 

 great numbers of large and beautiful spe- 

 cimens were obtained in tJie spring of 

 1830, although they have since entirely 

 disappeared. 



Planorbis campanulotus. — Say. 



Description. -Shell brownish or green- 

 ish yellow, finely striate ; whorls four and 

 a half, narrow, sub-carinate on the left 

 side ; inner whorls on this side scarcely 

 depressed below its plane, exhibiting- the 

 apex distinctly ; cavity of the right side 

 very profound ; inclination from a per- 

 pendicular to the left about 20*^; aperture 

 abruptly campanulate, oblique, including 

 the lower two-thirds of the height of the 

 penult whorl. Greatest breadth 0.51) inch ; 

 least breadth 0.45 inch ; height 0.27 inch. 



Remarks. -This species resembles some 

 small varieties of the precedlngl but is 

 distinguished by the abruptly campanu- 

 late aperture, and the narrowness of the 

 outer whorl, which in this species is 

 scarcely wider than the penult whorl, 



while in that species, owing to the rapid 

 enlargement of the whorls from the cen- 

 tre, the last greatly exceeds all the others. 

 Planorbis bicarinatus. — Say. 



Description. — Shell brown, or green- 

 ish horn color ; irregularly striate across, 

 with very sligiit revolving stria; ; whorls 

 three, carinate on i)olh sides, but more 

 acutely on the leftside; suture generally 

 coincident with the carinae except in the 

 la.st semi -volution on the right side ; con- 

 cavities of both sides equnlly deep, that of 

 the right wider ; inclination to the left 

 about 20=' ; aperture large, angtilated by 

 the left carina, embracing four-fifths of 

 the length of the penult whorl. Greatest 

 breadth 0.62 inch ; least breadth 0.44 in. ; 

 height of aperture 0.31 inch. 



Remarks. — This species inhabits both 

 quiet and running waters in ponds and 

 streams of every size. It is very common. 



Planorbis armigerus. — Sav. 



Description. — Shell brownish horn 

 color, feebly striate, shining ; whorls four, 

 subcarinate on the left side ; right side 

 slightly concave, left side deeply umbili- 

 cated ; suture distinct and well impress- 

 ed on both sides ; inclination to the left 

 about 40° ; aperture nearly orbicular, 

 slightly intruded upon by one-fourth of 

 the height of the i)enult whorl, very far 

 within armed with six teeth, of which 

 two are on the inner side, one on the mid- 

 dle, elevated, lamellar, oblique, tortuous, 

 large, the other just below it very small, 

 nearly conical ; four on the outer side, of 

 which the two left are large, elevated, la- 

 mellar, oblique, converging outwardlj', 

 the two on the riglit small, subconic, but 

 little elevated. Greatest breadth 0.34 

 inch ; least breadth 0.29 inch ; height of 

 aperture 0.13 inch. 



Remarks. — This species is remarkable 

 and singular in the genus for its teeth, 

 which have been elevated by Haldeman 

 to a generic character. It is common 

 among dead leaves in still water. In 

 swamps which are dried in the summer, 

 it then takes refuge in the moist earth and 

 leaves. 



Planorbis cxaciitus. — Say. 

 Description- Shell extremely thin and 

 fragile, brown, sometimes encrusted witli 

 a blackish substance, meniscoid ; whorls 

 four, carinate on the left side ; inner 

 Vv'horl on the right side slightly depress- 

 ed ; left side deeply umbiiicated ; last 

 whorl much broader than all the others, 

 convexly compressed on both sides to an 

 extremely acute, medial carina ; inclina- 

 tion to the left about 60° ; aperture large, 

 cordiform. Greatest breadth 0.24 inch; 

 least breadth 0. 1 inch ; height 0.056 inch. 



