502 LIMNiEIDJ:. 



A. tardus, Say, which has been found by Professor Adams in Ycr- 

 mont, but which I have not yet found in this State. It is much 

 more rounded and conical than this, and the apex is not lateral. 



Ancylus fuscus. 



Fig. 152, 



Shell oval, depressed, convexity regular, not compressed laterally, curvilinear 

 at the sides; apex obtuse, a little to the right and rear of the centre; epidermis 

 coarse, brown, surjjassing the margin. 



Ancylus fuscus, Adams, Bost. Journ Nat. Hist. iii. 329, pi. 3, fig. 17 (1840) ; Am. Journ. 

 Sc. [ij, xx.xviii. 396 (1840). — Haldeman, Men. 12, pi. 1, fig. 7 (1844). — Gould, 

 Inv. 224, tig. 152 (1841). -De Kav, N. Y. Moll. 13 (1843). — Anon. Can. Nat. ii. 

 212, fig. (1857). — W. G. BiNNEV, Smith. Inst. L. and Er. W. Shells, ii. 140, fig. 

 233 (1865). 



Shell small, very thin and pellucid, of a rounded oval form, the 



entire outline regularly curved ; depressed and regularly convex, 



not compressed at the sides ; apex slightly elevated, bluntly 



rounded a little behind, and to the right of the centre ; stages 



A. fits, of growth visible ; epidermis coarse and strong, rough, dusky 

 Enu'r ed yellowisli-browii, extending beyond the margin of the testa- 

 ceous matter, and insensibly coalescing with it on all sides, 

 which are inclined to turn upwards ; within glistening, polished. 

 Length, three tenths of an inch ; height, one twentieth of an inch ; 

 breadth, twenty-two one hundred and sixtieths of an inch. 



Found in a rivulet in Andover by Mr. K. Prescott, of the Theo- 

 logical Seminary ; and also found by Professor Adams in Mans- 

 field ; and by myself in Fresh Pond. 



It differs from all other described species in its depressed form, 

 its obtuse apex, and its coarse epidermis projecting beyond the mar- 

 gin ; and, as this extends in the direction of the plane of the object 

 to which it is found attached, and not in continuation of the convex 

 form of the shell, the edges seem to be turned upwards. A. paral- 

 hlns is narrower, and has the sides nearly parallel. A. tardus, Say, 

 has its apex prominent, acute, and farther behind the middle. 



[It has also been found in Ohio and the District of Columbia. 



