206 
AUG. F. FOERSTE 
17. Parallelodus obliqua Branson 
Plate XXI j fig, I 4 
A distinct and rather angular umbonal ridge extends from the 
beak toward the lower posterior angle. The post-umbonal slope 
is distinctly concave, especially toward the beak. The remainder 
of the valves, below and anterior to the umbonal ridge, is gently 
and evenly convex. There is no trace of a mesial depression or 
sinus. The ventral margin is gently and evenly convex for al- 
most its entire length, rounding more abruptly upward at the 
two extremities of the shell. The posterior margin of the shell 
is strongly oblique to the hinge-line, producing a rather narrowly 
rounded posterior angle. None of the specimens expose the 
teeth. The general appearance is that of Modiolopsis, but the 
absence of a mesial depression suggests the possibility of identity 
with Parallelodus. 
In Modiolopsis consimilis Ulrich (plate II, fig. 14, of this bul- 
letin), the ventral margin is nearly straight and the slope between 
this margin and the umbonal ridge is distinctly flattened. 
18. Cyrtolites ornatus minor Ulrich and Scofield 
Two forms of Cyrtolites occur near the top of the Plattin lime- 
stone in Ralls County. The largest specimens reach a diameter 
of fully 18 mm. Those specimens in which the transverse undu- 
lations meet the carina almost at a right angle are referred to 
Cyrtolites ornatus minor, while those in which the undulations 
curve strongly backward are regarded as a variety of Cyrtolites 
retrorsus Ulrich. 
19. Holopea cf. concinnula Ulrich and Scofield 
Plate XXI, fig. 7 
A specimen found at the top of the Plattin limestone at Conn^s 
Ford has about the same apical angle as typical Holopea concin- 
nula (plate XXII, fig. 7 of this bulletin), but the shell is smaller 
and the rate of enlargement of the volutions is less rapid. . 
