THE GEOLOGIST. 
NOVEMBER, 1858. 
PALiEONTOLOGICA.L NOTES ON THE BRACHIOPODA. 
By Thomas Davidson, Esq., F.R.S., Sec. G.S., &c. 
{Continued from page 416.) 
In our secood group are provisionally assembled a number of Tere- 
bratula-shaped species, with a curved hinge-line, no defined 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 
lamellae. 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 paloeontolo- 
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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