334 Deseriptiom of Neiu Species of Brachiopoda. 



rectiou ; socket ridges short, crenulated, oblique ; rounded, low, wavy 

 elevations just beyond the points and in front of the socket ridges ; a 

 small but rather deep pit immediately in front of the cardinal process, 

 from which extends a low mesial ridge to about the middle of the shell 

 forward, where it fades out ; the concentric wrinkles of the exterior 

 show through slightly, and the radiating strire plainly, with small, but 

 distinct, radiating rows of papilla, which are rather distant from each 

 other, to the ridge, but crowded together on the front slope and toward 

 the lateral margins ; no muscular scars observed. 



Width of a specimen of medium size, measuring from the points of 

 the hinge line, l^i\\ inch ; length, about three fourths of an inch. 



Position and locality : Cincinnati Group, about eighty feet above low 

 water-mark of the Ohio river, at Cincinnati. Collected by U. P. 

 James. 



Specimens of this shell were submitted to Mr. Meek, when he was 

 making up his report for the first vol., part ii., of the Paleontology of 

 Ohio. He considered it a variety of StropJiomena rhomboidalis, Wilck- 

 ens. Probably the material now at hand is better than he had for 

 comparison. Strophomena tenuistriata, Sowerby, he placed also as a 

 variety of S. rhomboidalis, and identical with S. gibbosa. Between 

 these three forms there seems to be wide variations. Some of the dif- 

 ferences are : 



The shell of S. tenuistriata is much thicker, the concentric wrinkles 

 stronger, and the radiating striae much coarser than S. gibbosa, and the 

 umbone more prominent. The interior of the dorsal valve of ^S'. 

 gibbosa, viewed posteriorly, shows the bifid cardinal process as erect and 

 at right angles with the plane of the shell, whilst it curves or leans 

 outwardly in the case of S. tenuistriata, and viewed from the front of 

 the shell the two parts are more spreading in S. tenuistriata than gib- 

 bosa ; the socket ridges much shorter and less prominent in tenuistriata 

 than gibbosa ; there is scarcely any depression immediately in front of 

 the cardinal process of tenuistriata, where the pit is quite decided in 

 gibbosa. Owing to the frail structure of the shell I have not been able 

 to procure a good interior view of the ventral valve of gibbosa for com- 

 parison, but the differences stated, together with the fact that S. 

 gibbosa is found only at a horizon about 80 feet above low water-mark 

 of the Ohio river at Cincinnati, and S. tenuistriata some 400 feet higher 

 in the rocks, and none of either species, that I have ever heard of, oc- 

 curring anywhere within or between these horizons, would seem to justify 

 its being placed as a distinct species. At any rate, if considered as 

 varieties only, they mark distinct horizons in the rocks in the west, 

 each holding its place constantly — S. gibbosa the lower nart of the Cin- 



