THE GEOLOGIST. 



NOYEMBEE, 1858. 



PAL^EONTOLOGIC^ NOTJiS ON THE BRACHIOPODA. 



By Thomas Davidson, Esq., F.R.S., Sec. G.S., &c. 

 {Continued from pige 416.) 



In our second group are proyisionally assembled a number of Tere- 

 bratula-shaped species, with a curved hinge-line, no denned area, beak 

 entire, or truncated by a circular foramen for the permanent or 

 temporary passage of a peduncle, and with spiral appendages directed 

 outwards, as in Spirifera, but connected by a more complicated system of 

 lamellffi. Much has, however, to be discovered concerning the interior 

 details of the larger number of the species before we can hope to 

 establish permanent and satisfactory divisions in this group. 



The genus Athyris has for years attracted the notice of palaeontolo- 

 gists, but it was not until a recent period that all its important 

 characters could be established. The species vary considerably in their 

 external shape ; they are circular or angular, elongated or transverse, 

 smooth, ribbed, or striated, some have the entire surface of their valves 

 covered with numerous concentric plates, which are prolonged in many 

 instances nearly an inch from the surface of the shell, while in other 

 species the valves are covered by a vast number of scaly ridges from 

 which radiate closely-set fringes of elongated, somewhat flattened 

 spines ; and so close are these sometimes in their arrangement, that no 

 portion of the shell can be distinguished. 



The beak of the larger valve is likewise at times so much incurved 

 over that of the smaller valve that for many years it was erroneously 

 imagined there existed no foraminal opening in the species of this 



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