CONTRIBUTIONS TO PALEONTOLOGY. 61 



specimens possessed are so few as almost to preclude examinations 

 of this kind. 



As an example of the diversity of internal structure in similar 

 external forms, I may mention the Terebratula altidorsata of Bar- 

 RANDE, which so nearly resembles the Centronella glans-fagea that 

 it might readily be mistaken for that shell. On cutting and ma- 

 cerating specimens of the fornier, they prove to possess internal 

 spires arranged as in Meristella, removing it from the family of 

 the Terebratulid^. I have not been able to determine positively 

 whether the shell of this species is punctate or fibrous, from the 

 specimens I possess ; but it appears to be fibrous, and is probably 

 allied to, or congeijeric with Meristella. 



5. OBSERVATIONS UPON THE GENUS STREPTORHYNCHUS, 



WITH REMARKS UPON SOME SPECIES HERETOFORE REFERRED TO THE GENERA 



STROPHOMENA AND ORTHIS. 



GENUS STEEPTORHYNCHUS ( King). 



# 



This genus, although published in 1850, has not, until recently, 

 been fully recognized by palaeontologists. Mr. Davidson, in Jiis 

 Introduction, has not considered the genus as distinct from Or- 

 THisiNA ; and upon this authority, some of the American species 

 have been placed under the latter, while other forms have been 

 described as Strophomena. 



The description of Prof. King is as follows : 



*' Diagnosis. A Strophomenidia : inoquivalved ; striated or rib- 

 *' bed ; with the hinge approximating or equal to the width of 

 " the valves. Umbones more or less divaricating; the large one 

 " irregularly twisted. Fissure covered with a deltidium. Dental 

 " plates small, projecting more at the base of the area than at 

 " its apex.'^ 

 " Type Terebratula pelargonata ( Schlotheim)." ' 



The characters here given, relating chiefly to external features, 

 induced the reference to this genus of such species as have the 

 beak of the ventral valve twisted or distorted, and the absence 

 of a full knowledge of the interior left other species among the 

 Strophomena. In some later investigations, Mr. Davidson has il- 



Monograph cf Permian Fossils, 1850, p. 107. 



