and of its Dependencies. 4<>1 



at right angles to the length of the shell. Edges of aperture slightly 

 thickened, and somewhat whitish. 



Length of young shell, 2 millimetres ; width, 1 m. ; height, .', m. 



The principal differences perceptible between this shell and the 

 Gruhdlachia Meekiama of Stimpson, are : — 



1st. The greater size ; Stimpson'a figure being only three millime- 

 tres long, while this is 5^ mill. 



2d. In G. Meekiana the right side is nearly straight, the truncation 

 of the posterior extremity is but slightly oblique, the right posterior 

 angle projecting; while in G. Stimpsoniana the left side is the straight - 

 est, the truncation posteriorly, is very oblique, the left angle pro- 

 j ecting. 



3d. In G. Meekicma the "smaller shell" is black, opaque, while 

 in G. Stimpsoniana it is amber-colored and very translucent. 



4th. Judging by the figure, in G. Meekiana, the "smaller shell" 

 appears to project more over the margin of the " large shell " than in 

 G. Stimpsoniana. 



5th. G. Meekiana is higher in proportion. A specimen of Q, 

 Stimpsoniana five and one-fourth mill, long would be two and one-tenth 

 mill, high, instead of one and one-half mill., if of the same pro- 

 portions. 



I examined several specimens of the animal while living, and was 

 unable, either in the young or the adult, to perceive any essential dif- 

 ference from that of the species of Ancylvs (A. fuscus ( '. B. 

 Adams) associated with them. 



This species occurred in three ponds at (Jreenport, and in one 

 on Shelter Island, opposite to that place. The specimens were 

 attached to floating sticks and logs, in company with two species 

 of Ancyhis, and were generally clinging to points very near the 

 surface of the water, and sometimes even a little above it, on spots 

 that were merely damp. The first specimens found, three years 

 ago, were of the young shell only, and similar ones occurred every 

 year since ; but it was not until dune, 1869, thai I found a very few 

 specimens presenting the adult form, and of these only two were 

 completely developed. The collections in previous years wen- all 

 made; at a somewhat later season (.July to September), and all the 

 specimens had the base covered by the septum to the extenl of two- 



