New Lower Silurian Ostracoda. — UlricJt. 267 
than Leperditia^ but I have satisfied myself fully that it, like the 
following species {L. dorsicornis), is an extreme development of 
the type begun in the stock that produced the L. wqui'latera, in- 
Jlata, and germami of this paper. From these species it is suf- 
ficiently distinguished by the more abrupt end and ventral 
slopes, and the greater development of the sulcus. 
Of the form that 1 propose, provisionally, to name as var. 
venfricoruis I have seen only the right valve illustrated. So far 
as I can see, the only .difference between it and the typical form 
of the species is found in the obtuse and retro rsely directed 
ventral prominence. 
Formation and locitUty: Associated with, but less abundant than, L. 
twnida, in the Bird^eye limestone at High Bridge, Ky. 
Lepepditia (? Primitia) dorsicornis, u. sp. 
Plate ix. Figs. 24 to 26. 
Length of a right valve, 1.72 mm.; hight, 1.1 mm.; greatest thickness 
(center of posterior half) 0.54 mm 
Valves subelliptical, slightly oblique, the ends subequal, the 
back straight nearly to the posterior extremity ; the latter is gently 
convex and almost vertical in the upper two-thirds, while in the 
lower third the outline merges rapidly into the uniformly convex 
basal margin; anterior end uniformly curved. Surface much the 
highest in the posterior half, with a part prolonged dorsally into 
a short and obtusely pointed prominence that bends down close 
to the hinge line and projects somewhat beyond it. This promi- 
nence gives definition to the posterior side of a distinct sulcus, 
extending almost half across the valve from the central part of 
the dorsal edge, and forward along the latter. 
This species ought, perhaps, to be called a Primitiahut for the 
reason given under L. sulcata I have chosen to designate it as 
above. Of the species believed to belong to the same line of de- 
velopment, L. injiata, seems to be the nearest. They are, however, 
readily distinguished by the concentration of the dorsal promi- 
nence and the greater definition of the sulcus in L. dorslcornu. 
Formation and locality: The only specimen seen was found in the 
Hudson River rocks at Savannah, Illinois. 
Leperditia granilabiata, n. sp. 
Platk IX, Figs. ?>\ to 3:5. 
Length, of right valve, 3.1 mm.; hight 1.52 mm.; greatest thickness 
0.6 mm. 
