2l8 THE AMERICAN MIDLAND NATURALIST 



elevated in front both on small and large specimens. Ventral area 

 low to moderately high, with the beak strongly incurved; foramen 

 large. Surface marked by fine striae running roughly parallel to the 

 plications of mesial fold and sinus very strong; lines of growth fre- 

 quent and strong. 



This variety might perhaps be justly designated as a new species, 

 as it is fully as distinct as many of the species of brachiopods that 

 are accepted — for instance some of the Atrypas. In its true form 

 there is no possibility for confusion with the true Spirijer 

 orestes Hall and Whitfield, but the two intergrade to such an extent 

 that for the present I designate the form Websteri as a variety. 



The differences from the Spirijer orestes of Hall and Whitfield 

 are in the greater size attained, the greater width in proportion to 

 the length, the greater depth of sinus and correspondingly greater 

 mesial elevation, the more pronounced character of both sinus and 

 mesial fold, and the greater coarseness of the plications and the 

 shell in general. The striae^ seem fewer on the surface of the shell in 

 specimens examined, but they do not differ in character from those 

 of the true species. 



Figure 26 shows a large and somewhat deformed specimen of this 

 variety. Figure 27 a smaller, finer, and proportionately wider 

 specimen with greater development of sinus and mesial fold. Figure 

 28 gives a detailed view of a portion of the dorsal and ventral valves 

 of a considerable smaller specimen than the one shown in 26, and 

 shows the coarseness of the shell, and the heavy lines of growth, 

 magnified. Figure 29 is a magnified detail of a portion of the sinus 

 of the same specimen use in figure 28, also magnified. This shows 

 the heavy lines of growth interspaced by smaller, lighter ones. 

 Figure 30 is an enlarged detail of the sinus of the specimen shown in 

 figure 27. It will be noted that two of the plications on the sinus 

 cease at the heavy growth-line or wrinkle. This same feature is shown, 

 but less plainly in the small figure, 27. Hederalla alternata (Hall 

 and Whitfield) is growing on the shell. Figure 31 is an enlarged 

 detail from the dorsal valve of the specimen shown in figure 26. 

 The portion shown is to the left of the sinus and mesial fold (right as 

 shown in the figure) and shows a bifurcation of the plications. The 

 plications on the right of the mesial fold are simple, and none of 

 the other specimens in the cotypes show bifurcation except on the 

 sinus and fold, as stated in the description. I am therefore inclined 

 not to regard this as more than an aberration. Another interesting 



