140 



After describing the genus, I cited as illustrations seve- 

 ral species from the Lower Helderberg group ; and gave 

 figures of the exterior of Meristella princeps and M. nasuta, 

 the latter species from the Upper Helderberg group. 



In the same Report I described three other species of 

 the genus, viz : Meristella haskinsi, M. barrisi and M. doris, 

 but without giving illustrations of these. 



Since, on the one side this genus has been claimed to be 

 equivalent to Athyris, and on the other, the same author 

 has placed some of its species under a later created genus 

 Charionella, it seems necessary to repeat some of the 

 characters of the genus in this connexion. 



Genus Meristella, Hall, 1860. 



The genus includes Terebratuloid or Athyroid forms which 

 are ovoid, more or less elongate, sometimes elliptical in out- 

 line, and not unfrequently transverse or sub-circular ; valves 

 unequally convex, w 7 ith or without a median fold and sinus, 

 and this feature usually confined to the lower half of the 

 shell. Ventral beak more or less closely incurved (when 

 closely incurved apparently imperforate), terminated by an 

 aperture, the lower side of which may be formed by the umbo 

 of the dorsal valve, or by a deltidium. Area none. 1 Valves 

 articulating by teeth and sockets. Surface smooth or marked 

 by fine concentric lines of growth, not lamellose, and in- 

 distinct or obsolescent radiating striae, which are usually 

 more conspicuous in the cast or exfoliated surfaces than on 

 the exterior. Shell fibrous. 



and some others of the Clinton and Niagara groups, differ somewhat from 

 true Merist.2e ; and should these differences prove of generic importance, I 

 propose for them the name Meristella." 



1 Those species with the ventral valve closely incurved are apparently im- 

 perforate, since no foramen is visible above the umbo of the dorsal valve. 

 In the separated valves of these species, I have not seen any deltidium ; an 

 open triangular space exists above the points of the dental lamellse, and this 

 communicates with the open cavity of the valve. 



