310 REPORT ON THE STATE CABINET. 



and will be adopted, I have no doubt ; but such a desirable end can only be 

 consummated after the study of the interiors of numerous specimens, with large 

 collections for comparison.* 



"Although having adopted the name Ehynchonella for our Devonian species, 

 I have lately observed characters which appear to me to separate them so widely 

 from the recent species of the genus, that I am compelled to substitute some 

 other designation. 



" Among genera of the same family we must necessarily make distinctions 

 upon the modifications of certain parts which they may all possess in common ; 

 and the importance of these modifications of interior parts or appendages should 

 not be overlooked. Not only do the recent and fossil forms referred to Ehyn- 

 chonella possess great similarit}^ in the ventral valve, teeth and dental plates, 

 but they are not very dissimilar from the same parts in genera of the Spiriferidse. 

 It is in the dorsal valve and its appendages that we find characters the most 

 important and reliable for generic distinction ; and it is onl;y necessary to follow 

 these in the genera of the Terebratulidaa and Spiriferidse to recall the most 

 curious and interesting modification of the parts which this valve supports. I 

 am therefore inclined to regard these modifications as of generic importance. 



" In manj' of the fossil species referred to Rhtkchonella, one of the most 

 conspicuous features in the dorsal valve is the strong septum, which becomes 

 broader, and often shows indications of division at the apex, or at least evidence 

 of a small and shallow V-shaped pit. 



" The recent species of Ehynchonella do not certainlj' furnish any evidence 

 of similar characters, so far as I have been able to examine specimens or illus- 

 trations. The dental plates of the ventral valve are not, it is true, essentially 

 difierent in fossil and recent Ehynchonella ; but the same comparison may be 

 made with other genera, even out of the family Ehynchonellidaj. 



" With these facts before us, I propose to revive the name Stenocismaj of 

 CoNEAD for the species under consideration, extending the term to include the 

 typical species lihynchonella formosa of the Lower Helderberg group." 



* The reliance upon external forms for the determination of generic affinities or differences, 

 although a compulsory condition, in many instances, is far from satisfactory. As an example of 

 this kind, I may remark that, having recently occasion to compare Terebratula sappho, Bar- 

 RANDB, with Rhjjnchonella sappho, Hall, the former presented so much of a rhynchonelloid 

 aspect as to suggest the propriety of regarding the latter as a synonym. A careful examination 

 of the Bohemian species, from cutting down the solid fossils, has revealed the fact that it is fur- 

 nished with calcarous spires arranged as in Atetpa, the spires directed into the cavity of the 

 dorsal valve, and the crura connected by a loop in a similar manner. 



tin his second Annual Report (page 59, 1839), Mr. Conrad, speaking of the rocks of New 

 York, says : " The Genus Terebratula is wholly unknown, and the shells usually " referred to 

 that genus I propose to group under the generic name of Stenocisma, derived from the two Greek 

 words signifying narrow fissure, a character these shells possess under the imperforate apex of the 

 larger valve, and which serves to connect the genus with Delthtris, from which it differs in having 

 no cardinal area. The last-named character, on the other hand, connects it with the Genus 

 Stetgocephalus. I refer to it the common Silurian bivalve Terebratula schlotheiinii, Von 



BUOH." 



Notwithstanding the assertion of imperforate apex, we have learned that many of these forms, 

 and probably all those which have been referred to Terebratula, have had, at some period of 

 their growth, a perforate apex. It was also a Lower Helderberg species {lihynchonella formosa') 

 which was referred by Sir. Conrad to "the common Silurian bivalve T. schlotheimii." I have 



