270 TWENTIETH REPORT ON THE STATE CABINET. 



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 Rhynchonella 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 Rhynchonella possess great similarity in the ventral 

 Talve, teeth and dental plates, but they are not very dissimilar from the 

 same parts in genera of the Spiriferid^. It is in the dorsal valve and 

 its appendages that we find characters the most important and reliable for 

 generic distinction ; and it is only necessary to follow these in the genera 

 of the Terebratulid^ and Spiriferid^, 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 many of the fossil species referred to Rhynchonella, one of the 

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

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

 least evidence a small and shallow \/-shaped pit. 



'The recent species of Rhynchonella do not certainly furnish any 

 evidence of similar characters, so far as I have been able to examine 

 specimens or illustrations. The dental plates of the ventral valve are not, 

 it is true, essentially different in fossil and recent Rhynchonella ; but 

 the same comparison may be made with other genera even out of the 

 Family Rhynchonellid^. 



' With these facts before us, I propose to revive the name StenocismaI 

 of Conrad for the species under consideration, extending the term to 

 include the typical species Rhyncho7iella formosa of the Lower Helderberg 

 group.' 



• *The reliance upon external forms for the determination of generic affinities or diflfer- 

 ences, although a compulsory Jcondition in many instances, is far from satisfactory. As 

 an example of this kind, I may remark that having recently occasion to compare Terehra- 

 tula Sappho, Barrande, with Rhynchonella 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 furnished with calcarous spires arranged as in Atrypa, the 

 spires directed into the cavity of the dorsal valve, and the crura connected by a loop in 

 a similar manner. 



■j- *In 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 

 ^'referreid to that geuus 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 Delthyris, from which it differs in having no cardinal area. This last- 

 *' named character, on the other hand, connects it with the Genus Strygocephalus. I 

 *' refer to it the common Silurian bivalve, Terebratula schlotheimii, Von Buch." 



' 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 

 8ome period of their growth, a perforate apex. It was also a Lower Helderberg species 



