NOTICE OF PALEONTOLOGY OF NEW YORK. \%l 



centric striae, and some of them are strongly lamellose, with the lamellae 

 becoming fimbriate or pectinate. In this aspect, as well as in general 

 form, these shells have a resemblance to some of the Spirifers with short 

 area and rounded cardinal extremities. The surfaces are sometimes 

 obscurely radiatingly striate ; but these striae are usually subordinate to 

 the concentric stride or lines of growth, and it may be doubted whether 

 any well authenticated species of the genus has conspicuous radiating 

 striae or costae. 



The apex of the ventral valve is usually or perhaps always perforated 

 by a rounded foramen, the lower side of which is formed by the umbo 

 of the opposite valve. When the valves are separated, this foramen 

 communicates with a triangular space which opens into the main cavity 

 of the valve. This triangular fissure, which in older shells is usually 

 occupied by the beak of the opposite valve, has at some time during the 

 animal's life been closed by deltidial plates. 



The dorsal valve is furnished with a strong cardinal process, the centre 

 of which is often depressed and spoon-shaped, but sometimes thickened 

 and convex. The crura proceed from each side of this plate anteriorly ; 

 while the posterior and lateral margins become more or less thickened, 

 or elevated into ridges bordering the teeth-sockets. 



The muscular area is somewhat variable in form ; but in the ventral 

 valve it is oval or ovate, more or less flabelliform. The occlusor muscu- 

 lar imprints are marked upon the shell, and upon the cast, by a narrow 

 elongate scar ; while the divaricator muscles occupy a wider space on 

 each side, and are usually strongly striated. In the dorsal valve the 

 muscular area is narrow, and often divided by a low longitudinal crest 

 or septum. The space outside of the muscular scars is papillose or 

 papillose-striate, and often beautifiiUy marked by vascular impressions. 

 The spires are complicated by intermediate lamellae. 



The European species of Athyris (^A. pectinifera, A. roissyi and A. con- 

 centricci), as shown by Woodward, Davidson and others, have the spires 

 complicated by accessary lamellae, which, rising from the connecting 

 loop, are intercalated between the first and second turns of the normal 

 lamellae, and have their extremities free. 



Although the presence of spires has been long known in the American 

 species, I believe no one has hitherto shown their analogy with the 

 European forms. In the determination of our species, however, and 

 their relations with Meristella, it became necessary to make a careful 

 study of all the internal characters upon which generic and specific dis- 



