SOME NEW BRACHIOPODS AND GASTROPODS 215 



latter most characteristic, defined on their margins by a thickening 

 of shell, while deep, irregular, linear impressions continue to the 

 margin of the shell. Cardinal process prominent, bilobed, with a 

 deep impression for the "horns" of the dorsal cardinal process. 



This variety differs from the Strophonella reversa of Hall in its 

 generally heavier character, greater coarseness of the shell, greater 

 height of the dorsal valve and greater length in proportion to the 

 width. In the interiors of both valves this coarseness and heaviness 

 is very apparent. It also differs from the true Strophonella reversa 

 in that the valves are seldom produced along the margin to any 

 extent, as is frequently the case in the form described by Hall. 



Cotypes: — Set 901, collection of C. L. Fenton, Spirifer zone, pits 

 of the Rockford Brick and Tile Company, Roekford, Iowa. 



Douvteuna arcuaTa maxima no v. var. 



Shell semielliptical; hinge line barely or not equal to the greatest 

 width of the shell. Ventral valve hemispheric very gibbous near 

 middle; beak slightly to quite pronounced. Dorsal valve 

 quite concave, but not so deeply as in the typical species. 

 Area common, with that of the ventral valve the larger, and bearing 

 deep vertical striae . In all specimens examined by me there is no 

 foramen. 



Surface of shell marked by strong striae "or which sometimes 

 consist of a few strong ones near the beak, bifurcating below, while 

 the general character of surface marking is that of strong, sharply 

 elevated striae with three, four, or five smaller ones between" 

 (Hall, original description). I have noted this characteristic, and 

 it is shown very well in specimens in a set from Rockford in the 

 collections of the University of Michigan. As a rule, however, the 

 striae on the surface of maxima are less pronounced, and more 

 inclined to be simple than in the typical species. The interior of the 

 shell does not differ greatly in general markings from the species 

 arcuata of Hall, but is considerably heavier and coarser. 



This variety differs from Douvellina arcuata (Hall) in the larger 

 size attained, the greater width in proportion to length, the heavier 

 character of the shell and greater thickness. It is genendly a more 

 robust form, and while not differing greatly in a written description 

 differs much in the specimens. A comparison with the figures 

 given and the figures accompanying Hall's description of Strophodonta 

 arcuata will serve to bring out more plainly these differences. 



