38 [Assembly 



OBSERTATIONS ON THE GENUS RENSSELiERM. 



The species wliicli I liave grouped under this designation, have, in 

 some of their forms, been described as Terebratula, Atrypa and 

 Pentamerus, and more recently I have referred them to Megante- 

 ris; to neither of which genera do they belong. One of the most 

 common species in the Oriskany sandstone attracted attention in the 

 collections which were made at the Helderberg mountains forty 

 years ago, and specimens are preserved in the " Clinton Collection" 

 of the Albany Institute. Professor Amos Eaton, in his Geological 

 Textbook published in 1832 (p. 45), recognizes two species which 

 he' notices as Terebratula ovoides and T. perovalis; but since he re- 

 marks that they are found " also in all parts of Europe in the same 

 rock," it is to be presumed that he regarded these forms as identical 

 with the European species of the same names. 



In 1839, Mr. Conrad described the more common form from the 

 Oriskany sandstone as Atrypa elongate* ; a name adopted by the 

 geologists of New-York, and perpetuated in their reports. He also 

 describes a species of this genus, from the Lower Helderberg group, 

 as Atrypa cequiradiataf . 



In 1843, Mr. Vanuxem described a species of this genus, from the 

 Upper Helderberg limestone, as Pentamerus elongataX. 



These fossils, though presenting considerable variety when com- 

 pared in their extreme forms, nevertheless constitute a very natural 

 and beautiful group, easily recognized both in their external and 

 internal characters||. 



* Annual Report on the Palseontology of New-York, 1839, p. 65. 



I Journal of the Academy of Natural Sciences, Vol.viii, 1842, p. 266. 



X Geological Report of the Third District of New-York, 1843, pp. 132 & 133, f. 1. 



II In 1855, after having stiidied the exterior of the shell and its structure, together with 

 the easts which I had obtained in New-York, I proposed for these fossils a distinct generic 

 designation; but receiving, soon after, Mr. Davidson's paper "On the systematic arrange- 

 ment of recent and fossil brachiopoda," published in the Annals and Magazine of Natural 

 History for December 1855, I observed for the first time, in the accompanying improved table 

 of genera, the name of Meganteris (Suess), with a reference to Terebratula archiaci as 

 the type of the genus. The figure given in the Palseontographica so much resembles the casts 

 of some of the Rensseleeriae, that I inferred the two to be identical, and have thus described 

 these fossils in my paper published in the Rfigents' Report for 1856 (Palasozoic Fossils, 1857) ; 

 and it was not until recently (1858) that my correspondence with Mr. Davidson and Mr. 

 Stjess, and the reception of the paper of Mr. tSuESS on the Genus Meganteris, with il- 

 lustrations, has satisfied me that this genus is quite distinct from the Renssel^ria. 



