154 FIFTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



OBSERVATIONS UPON A NEW GENUS OF BRACHIOPODA. 



In the Thirteenth Report of the Regents on the State Cabinet of 

 Natural History, page 69, I called attention to the characters of 

 Atrypal modesta, and the internal spires of that fossil. I have lately 

 received, through the kindness of Dr. Charles Rominger of Ann- 

 Arbor, Michigan, some very interesting specimens of this species, 

 in which the direction and relations of the internal spires appear 

 to be fully shown. The crura spread from the rostral cavity almost 

 rectangularly towards the lateral margins, curving with the shell to 

 near its base ; and thence recurving, they make about three volu- 

 tions, with the apices of the spires directed obliquely into the cavity 

 of the dorsal valve. The outer limbs of the two spires are connected 

 by a band, or loop, stretching across the entire space with a gentle 

 curve towards the beak, and exterior to the spires on the'dorsal side. 



The direction of the spires is nearly the same as in Atrypa, differing 

 in the presence of the strong loop; while the shell, in its exterior 

 character, is quite unlike Atrypa. In two specimens examined, there 

 is a slight variation in the direction and extent of the loop. In one, 

 it rises from below the middle of the outer curve of the spiral, and, 

 curving gently, passes over the apices of the spires. In the other, 

 the origin of the loop appears to be at a higher point, or otherwise 

 it lies parallel with the outer curve of the spiral for some distance, 

 and stretches from one side to the other between the spires and the 

 base of the crura. This difference may be accidental, or may be 

 caused by displacement of the loop in one case : in both, however, 

 the essential features are preserved. 



For the Brachiopoda of this character, I propose the name Zygo- 



SPIRA*. 



GENUS ZYGOSPIRA (n.g.). 



Shells bivalve, equilateral, inequi valve : surfaces plicate in the 

 typical species; a sinus on the dorsal valve. Internal spires ar- 

 rangejl somewhat as in Atrypa, with a broad loop passing from 

 the outer limbs of the spiral band antirely across from side to 

 side, near to or above the centre, and close to the inner side of the 

 dorsal valve. 



* Gr. C,vyog, jiigum; oneipa, spira. 



