Art. VII. Observations upon some of the Brachiopoda, with 

 reference to the genera Cryptonella, Centronella, Meristella, 

 and allied forms, by J ames Hall. 



[Read before the Albany Institute, February 3d, 1863.] 



Abstract. 



In the study of the Palaeozoic Brachiopoda, we are often 

 forced to rely upon the general external form, and texture 

 of the shell, for determination of the generic relations, 

 until more extensive collections may furnish us with 

 weathered specimens, or with crystalline or silicified ones, 

 which, admitting of being cut; and macerated in acid, will 

 enable us to ascertain the true interior characters. 



In many instances, so nearly do very distinct genera ap- 

 proach each other in their external form, that reliance on 

 this alone is very uncertain, and will surely lead to much 

 confusion, if insisted upon as the means of generic deter- 

 mination. 



For a long time, and until we began to learn something 

 of interior structure, a large number of species, now 

 known to belong to distinct genera, were embraced in the 

 designation, Terebratula and Atrypa. At a later period, 

 when the Genus Rhynchonella had been established in its 

 application to many palaeozoic forms, we find numerous 

 species, which from external form had been referred to 

 that genus, possessing characters incompatible with it. 



One of the most common of these is Terebratula cuneata— 

 Rhynchonella cuneata— Retzia cuneata, and which will probably 

 be found to differ from true Retzia, taking its place near 

 Rhynchospira. 



So long as we remain unacquainted with the interior of 

 the shell, we are compelled to refer the species to some 

 genus having similar external forms, though the fibrous or 

 punctate texture may in many instances prove a valuable 

 aid in these references. 



[Trans iv ] 17 



