OSTRACODA. 637 
Leperditella canalis. ] 
Prof. T. Rupert Jones recently described two species from Canada (Contri. Can. 
Micro-Pal., pt. 3, 1891), that may be congeneric with these species, viz.: Leperditia 
? obscura and Isochilina labellosa, the latter appearing to be much like L. tumida. 
LEPERDITELLA CANALIS, 1. Sp. 
PLATE XLITI, FIGS. 1—3. 
Size,—Leneth, 1.78 mm.; hight, 1.22 mm.; thickness (L. V.) 0.59 mm. 
Carapace ovate, widest posteriorly, tumid, the point of greatest thickness but 
little behind and beneath the center; anterior outline semicircular; dorsum straight, 
not angular in front, and quite obtuse behind, posterior margin somewhat obliquely 
rounded, scarcely truncated above; near the ventral edge of the left valve a distinct 
channel or groove, deepest centrally, has suggested the name. Surface smooth. 
This species is closely related to L. twmida Ulrich, occupying a similar geological 
position in Kentucky and Tennessee, and of which a right valve is figured for com- 
parison on plate 45, (figs. 13—15), The outline in that species however is not so 
regularly rounded in front, nor so full antero-ventrally, the greatest convexity is 
more posterior and scarcely so great, and the dorsal angles more distinct. But the 
feature particularly relied on in distinguishing the two species is the groove along the 
ventral border of the left valve in L. canalis, the Kentucky form being without this 
pecuharity. 
Formation and. locality.—Lower limestone of the Trenton formation, Minneapolis, Minnesota. 
LEPERDITELLA PERSIMILIS, 2. Sp. 
PLATE XLIll, FIGS.4—6, 
SizE.—_(B. C.) Length 1.75 mm.; hight 1.23 mm.; thickness 0.8 mm. 
Carapace ovate, moderately convex, with the ends nearly equal; no dorsal angle 
behind but a well marked one in front; ventral overlap distinct; dorsal edge thick, 
shoulder like; greatest thickness central; suface smooth. The length varies between 
1.5 mm. and 2.5 mm. 
At first sight this species looks very much like L. canalis, but carefully compared 
they prove quite distinct. The outline is somewhat different being less wide (high) 
posteriorly, the dorsal angles are reversed, and the dorsal edges much thicker, while 
the thickness of the carapace is less and the ventral groove, which marks the left 
valve in that species, wanting. Similar differences distinguish it from L. twmida. 
Aparchites ellipticus holds about the same size and is not very different in outline. 
Still as its valves do not overlap ventrally and as it has no dorsal angles and really 
