148 PALEONTOLOGY OF NEW YORK. 



the spirals to produce an equal inclination outwardly. As to the loop, there 

 is as yet no satisfactory proof of its existence ; indeed, the evidence derived 



FlO. 185. FlQ. 186. 



The brachidiam'of Cydotpira bimlcata, Emmons. (C.) 



from a number of transparent preparations is decidedly negative upon this point. 

 Where the crura are attached to the primary lamellae, the ribbon is broadened, 

 and just in front of these points there appear to have been two short convergent 

 apophyses which may be construed as discrete elements of a loop. Though an 

 unprecedented occurrence, it would not be surprising or unnatural to find this 

 early gpirigerous shell actually ajugate. Subsequent investigations of the 

 brachidium must be relied upon to determine whether or not the loop was ever 

 a continuous lamella, but hitherto, repeated preparations of the brachial appa- 

 ratus have given no satisfactory evidence of such a structure.* 



The peculiarities of the internal supports combined with the nature of the 

 hinge-plate and the contour and smooth exterior of the shell, make an associa- 

 tion which removes Alrypa bisulcata from any intimate connexion with Zygos- 

 PiBA, Catazyoa and Glassia, in which the spirals are also introverted, and 



* Specimens of Atrypa biiulcata in a suitable condition for the determination of the internal characters 

 are rare. When the matrix is opaque, it usually consists of a mass of organic debris which bos brulien 

 down the delicate brachidium. Through the kindness of Mr. W. R Billings, of Ottawa, we have been 

 permitted to examine an extended series of specimens from his collection and to select for cutting such 

 aa poaacoaod a translucent filling, and upon these the determinations have been based. 



