JONES.] PALEOZOIC OSTRACODA. 81 



Leperditia haltica, Schmidt. Mem. Acad. Imp. Sci., St. Petersbourg, Ser. 7, 



vol. XXXI, No. 2, 1875, p. 15; and ibid. vol. XXXI, 

 no. 5, 1883, p. 11, pi. i, figs. 2 and 3. 



Length, (hinge-line), height, thickness of carapace. 



Fig. 12 10.7? (8.7?) 7. 4. mm. 



Fig. 13 8.6 7. 5.3 3.3 mm. 



Baltic specimen, 1856 20. (15.) 13. 9. mm. 



This has the usual Leperditian form; and, though half the size, 

 closely resembles that o^ Leperditia balthica, especially the figures given 

 by F. Schmidt, above-quoted. Our fig. 13 a represents a perfect small 

 left (the overlapped) valve, having a rather more strictly oblique ven- 

 tral margin, and with the submedial convexity rather lower down in 

 the valve, than Schmidt's figs. 3 «, 6 ; and it has a marginal thicken- 

 ing or narrow swelling at the posterior moiety of the hinge-line, some- 

 what like that in Ij. glbbera, Jones, but thinner and longer, being equal 

 to a third of the valve's length. 



Our figs. 12 a, b, of a right (the overlapping) valveof larger growth, 

 though not in perfect preservation, show a thickening on the edge of 

 the ventral margin, where it is turned in, and a rather bolder postero- 

 ventral curvature than in either Schmidt's (1875), or my ow^n figures 

 (1856). In both fig. 12 and fig. 13 the eye-spot and its escutcheon, 

 and the muscle-spot are very apparent. There is also a small left 

 valve which is somewhat gibberous (slightly swollen at its dorsal edge.) 



The relatively small size of these valves, the marginal thickening of 

 the ventral border in one, and of the dorsal border ia the other, — and 

 the full postero-ventral curve of the right valve, though non-essential 

 differences from the type, are worthy of notice, — and give cause for 

 this form to be regarded as a variety (Yar. guelphica). It may be 

 added that the strong backward and downward ventral curve a],- 

 proaches that of X. Hisingeri ; but, there being no hollow ogee curve 

 below the postero-dorsal angle, the hinge-line is relatively longer than 

 in that species, and its proportion is thus kept nearer to that in L. 

 balthica. The proportions closely approach those of some specimens 

 of L. gibbera, Jones. The left valve of Baron von Toll's L. Kotelnyensis, 

 Mem. Acad. Imp. Sci., St.-P^tersbourg, Ser. 7, vol. XXXVII, no. 3, 

 1889, p. 42, pi. iii, fig. 9 a, has much resemblance to our fig. 13 a ; but 

 it is longer, and its postero-ventral region is not nearly so full, nor so 

 oblique. Both have a mai-ginal thickening in the postero-dorsal re- 

 gion ; but the posterior dorsal angle is much more pronounced in our 

 figs. 12 and 13 than in von Toll's fig. 9 a. 



A few specimens of casts of valves, retaining remnants of the test, 

 from the Guelph Limestone of Durham, Ontario, have been supplied 



