SOME NEW BRACHIOPODS AND GASTROPODS 219 



aberration is shown in figures 27 and 30, where the sinus loses some 

 of its plications at the heavy growth-wrinkle. 



Cotypes: — Set 265, collection of Carroll Lane Fenton. Spirifer 

 zone, pit of the Rockford Brick and Tile Company, Rockford, Iowa. 



Spirifer Whitneyi rockfordensis nov. var. 



Shell of medium size, valves strongly convex. Ventral valve of 

 holotype with sinus marked by eleven dichotomizing plications, 

 mesial fold by eleven (or twelve?). Sinus concave near beak, but 

 becomes strongly convex toward fore part of the valve; mesial 

 fold very highly elevated. Surface of shell marked by about twenty- 

 five plications on either side of the fold and sinus, plications finer 

 than in the typical S. Whitneyi of the same horizon, but with 

 comparatively wide spaces between. Beak strongly incurved over 

 a low area bearing vertical striae. Plications marked by fine 

 radiating striae. Hinge line and width of shell small. In the holo- 

 type the hinge line does not exceed the width of the shell. 



This variety differs markedly from the species as described by 

 Hall. The width is much less and the thickness of the shell much 

 greater, the beak is much more strongly incurved, and the area much 

 narrower. The dorsal valve is much more gibbous and much larger 

 in proportion to the ventral than in the typical form. The sinus is 

 very abrupt, and its convex character is very distinctive. The 

 holotype, which is the only specimen in my collection that can be 

 positively referred to this variety is somewhat larger size than the 

 average Spirijer Whitneyi, and is apparently an aged specimen. It 

 is considerably worn and bears borings of a Cliona, apparently 

 C. hackberryensis Thomas. This variety is not to be confused with 

 the mutant 5. whitneyi gradatus described below. 



Holotype: — Number 236, collection of C. L,. Fenton. Spirifer 

 zone, pit of the Rockford Brick and Tile Company, Rockford, Iowa. 



Spirifer Whitneyi gradatus nov. mutant. 



Shell of medium size, with plications similar to the typical Whitneyi, 

 as to number and arrangement, but considerably coarser and with 

 the spaces between greater. Sinus broad, abrupt and usually deep 

 and sharply defined. The mesial fold is regularly correspondingly 

 high, and well defined. The beak of the ventral valve is sharply 

 curved, the area correspondingly low. The hinge line is about 

 equal to the width of the shell, though there is sometimes a tendency 



