OSTRACODA. 639 



Leperditella dorsioornis ] 



Leperditella. ? DORSicoENis Ulrich. 



PLATE XLV, FIGS. ID, 20 and 20o. 



Leperditia f (Primitia) dorsioornis Ulkich, 1892. American Geologist, vol. x, p. 267. 

 Size.— (L. V.) Length 1.72 mm.; hight 1.1 mm.; thickness 0.54 mm. 



Valves subelliptical, slightly oblique, the ends subequal, the back straight nearly 

 to the-posteripr extremity; the latter is generally convex and almost vertical in the 

 upper two-thirds, while in the lower third the outline merges rapidly into the uni- 

 formly 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 prominence 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. 



Though having a sulcus, and therefore agreeing in a general way with Primitia, 

 I have chosen to arrange this species with Leperditella because it seems to represent 

 merely ah extreme development from such typical species of the genus as L. inflata, 

 L. germana and L. sulcata. Specifically the present form is readily enough distin- 

 guished by the concentration of the dorsal prominence, and greater definition of the 

 sulcus. The form which I called Primitia glabra* and which occurs in the upper 

 beds of the Cinciiinati group in Ohio and Indiana, has a similar outline, but it is 

 somewhat smaller and without the dorsal prominence. Still, I would not be sur- 

 prised to find that it has overlapping valves as in Leperditella. 



Formation and locality. — The type was found in the Hudson River shales at Savannah, Illinois. As 

 equivalent strata occur near Wykoff and Spring Valley, Minnesota, it is quite likely that the species 

 occurs also in this state. 



Genus SCHMIDTELLA. Ulrich. 



Schmidtella, Ulrich, 1892. American Geologist, vol. x, p. 269. 



Carapace small (2 mm. or less in length), short, rounded or subovate, moderately 

 convex, more or less infiated in the dorsal region, this part being the thickest and 

 appearing generally (in an end view), as projecting shoulder-like over and out from 

 the straight hinge line; right valve slightly larger than the left and overlapping it 

 along the ventral margin. No eye tubercle nor sulcus, but a faint central pit and 

 elevation occasionally present. 



Type; S. crassimarginata, Ulrich. 



* Jour. Cin. Soc. Nat. Hist., vol. xili, p, 134; 1890. 



