154 



TWENTIETH REPORT ON THE STATE CABINET. 



The internal spires of this species, in their first volution and in the acces 

 sary lamellge, are quite distinct from those of A. spii'iferoides . The accom- 

 panying figure is an illustration of the first volution of the spires, with the 

 accessary lamellse. 



Athtris vittata. 



Central portion of the spires. 



The bases of the crura are shown at a, and these projecting a short dis- 

 tance forward make a somewhat abrupt retral curve, turning back in the 

 direction indicated by the dotted lines h ; and thence descending into the 

 cavity of the dorsal valve, follow essentially the curvature of its outline, 

 as indicated at c, to a point anterior to the middle of the length of the spi- 

 ral curve. Here the branches of the loop are given off at d ; and these pro- 

 jecting vertically into the cavity, are turned abruptly forward, and beyond 

 the (lotted line, form a solid pointed plate which projects far towards the 

 anterior limits of the spires at e. The posterior portions are produced back- 

 wards, and gradually ascending, continue parallel and in close proximity as 

 far as /, where they diverge, sending off a fillet on each side which at g 

 assumes the curvature of the normal lamellae of the spire, following the 

 same course into the cavity of the valve, and extending forward to the 

 origin of the process forming the loop, they are united to the proper spiral 

 lamellae at A, which then continue simple as shown in their extension to i. 



A second species in the Hamilton group is the Athyris cora. In the Che- 

 mung group, we have the Athyris angelica and the A. ? polita. 



The Genus Meristella, separated from Athyris on account of its 

 different external characters and muscular impressions is represented as 

 follows : 



Meristella nasuta, in the Schoharie grit and Corniferous limestone ; 



M. scitula, ) • ,1 n -i" T + 



Tij- /7 • ( in the Corniierous limestone; 



M. barrisi, ) 



M. haski?isi, > in the Hamilton group ; 



M. rostrata, ) 



M. meta (n. s.). 



