182 PALEONTOLOGY OF NEW YORK. 



Observations. No more decisive evidence of the close generic relations of 

 Orthis and Rhynchonella than is furnished by this species, can be desired or 

 expected. The shell is, in effect, a Platystrophia with shortened hinge, nar- 

 rowed and acuminate beak, and well-developed crural processes ; or the propo- 

 sition is convertible ; it is a Rhynchonella, with cardinal areas and uncovered 

 delthyria on both valves. There is a singular anachronism in the sole appear- 

 ance of this type of structure at a period so long after the distinctive ingredient 

 stocks were well established, a fact which may, to some degree at least, be 

 ascribed to our incomplete knowledge ; at the same time there is an eminent 

 fitness in the concurrence of this PLATYSTROPHiA-like Rhynchonella in a fauna 

 with Platystrophia itself, at its highest and most varied development. 



Orthorhynchula Linneyi is rather widely distributed in the Hudson River fauna 

 of Kentucky, but is not known to the eastward. 



Genus RH YN C HOTRE M A, Hall. 1860. 



PLATE LVI. 



1842. Atrypa, Conkad. Journal Acad. Nat. Sci. Philadelphia, vol. viii, p. 2(j4. 



1847. Atrypa, Hall. Paljeontology of N. Y., vol. i, pp. 146-148, 289, pi. xxxiii, tigs. Via-y, \ia-c; 

 pi. Ixxix, tig. B. 



1859. Rhynchonella, Hall. Twelfth Ann. Rept. N. Y. Slate Cah. Nat. Hist., pp. 65, 66. 



1860. Rhyiichotrema, Hall. Thirteenth Ann. Kept. N. Y. State Cab. Nat. Hist., pp. 66-68, figs. 8-13. 

 1873. Rhynchonella, Mehk. Palaeontology of Ohio, vol. i, p. 123, pi. xi, tigs. 6 a-f. 



187.5. Trematospira, Miller. Cincinnati Quarterly Journal of Science, vol. li, p. 60. 

 1889. Rhynchonella, Nettelroth. Kentucky Fossil Shells, p. S3, pi. xxxiv, figs. 26-29. 



This name, introduced more than thirty years ago, was designed to indicate 

 a peculiar variation in structure, which is not often retained even in the type- 

 species itself, though its absence is unquestionably due to accidental causes. On 

 this account, perhaps, the term Rhynchotrema has failed of general adoption, 

 and it is only quite recently that some writers* have indicated a disposition to 

 employ it. 



* See Waagen, Salt-Range Fossils, p. 410. Dr. Waagen, taking as of prime importance the alisence of 

 dental lamellse in the typical species, has suggested the occurrence of the group among the American De- 

 vonian Rhynchonellas. Probably, however, the type of structure, of which the lack of dental lamellie is 

 but a single element, was more n.arrowly restricted in its vertical range. CEhlert, in Fischer'.s Manuel de 

 Conchyliologie (1887), has also used the term, and accompanies it with some original figures, used in a pre- 

 vious publication (Bull. Soc. G6ul. de France, 3" Ser., t. xii, p. 426, pi. 10, a, h), but which fail to show the 

 critical characters of the genus. 



