IXVKKTEBRATKS. 105 



Surface ornamented with numerous concentric striae, or fine 

 liii^s of growth that are most conspicuous on the borders of 

 the shell. 



Length ir> , inch: greatest breadth 9 / le inch. 



This species resembles in its general form the L. mrtiloides of 

 the Coal Measures, but differs from that in its uniformly much 

 larger size and relative proportions. 



Hare, and hitherto found only in the Warsaw beds of the St. 

 Louis group at Warsaw and near Hamilton, 111. 



Collector. A. H. Wort hen. 



No. 2495 of the Illinois State Museum. 



GENUS SPIKIFEKA. Sowerby. 

 SPIHIFERA MLXTIGRAXOSA. (sp. nov.) 



PL XI, Figs. 5-oa, 5b. 



Shell of medium size, ventral valve strongly convex, length a 

 little more than the width: hinge line about equal in length to 

 the greatest width of the valve. Beak strongly arched, and re- 

 curved beyond the cardinal area. 



A profound sinus commences at the beak, and gradually widens 

 and deepens to the frontal border where it occupies about one- 

 third of the entire width of the valve. There are two rather 

 obscure costte on each side of the sinus, one of which extends 

 nearly to the beak, while the other becomes obsolete about half 

 way from the frontal margin to the beak. On each side of the 

 sinus there are from 8 to 10 unequal sized rounded plications 

 that are wider than the intervening spaces. Cardinal area 

 moderately wide. 



Dorsal valve less convex than the ventral, beak depressed, in- 

 curved, and not projecting beyond the hinge line, area narrow. 

 A strong mesial fold commences at the beak with a rather broad 

 flat cost a. having a central depression that continues to the 

 frontal margin. On each side of this there is an obscure costa, 

 that becomes obsolete before reaching the beak. The two first 

 plications on each side of the mesial fold are much stronger 

 than those on the lateral borders. The entire surface of the 



shell is thickly set with small granules. 

 -13 



