( I. ) 



OBSERVATIONS ON THE INTERNAL APPENDAGES OF THE 



CxENUS ATRYPA; 



With a Notice of the Discovery of a Loop, connecting the Spiral Cones. 



By B. p. WHITFIELD. 



The internal appendages of the genus Atrtpa {Dolman)^ have long been 

 known to consist of a pair of spiral cones, placed side by side, with 

 their apices directed towards the cavity of the dorsal valve. The lamellse 

 forming these cones have been described and figured as having their 

 origin on the socket- walls of the dorsal valve, then suddenly deflected 

 outwards, running parallel with the inner margin of the valve. At the 

 point where they are abruptly deflected, is figured a pair of short, pointed, 

 crural processes, directed toward each other, but not connected. 



This appears to be all that has hitherto been known regarding these 

 appendages ; although, judging from analogy, we might reasonably 

 suppose that, as most genera of Brachiopods having spiral cones have 

 been found to possess some sort of loop or crural process connecting them, 

 that Atrypa would not be destitute of some similar arrangement. 



By carefully cutting and preparing favorable specimens, I have found 

 that in place of the short crural processes so often figured, there is an 

 entire and continuous loop connecting the spiral cones, in a very similar 

 manner to that shown by Prof Hall to exist in his genus Zygospira, but 

 having its connection with the spiral ribbons, at a point relatively much 

 nearer to their origin on the hinge-plate ; still more distant, however, 

 than the points figured by Mr. Davidson and others. This loop, so far 

 as yet observed, is confined to the rostral or posterior part of the shell, 

 and never passes over or in front of the spires as in Prof. Hall's genus. 

 From its origin on the posterior portion of the first volutions of the 



