JONES.] CANADIAN MICRO-PALyEONTOLOGY. 79 



tically curved below ; ends rounded, narrower (lower) in front than 

 behind, but a left valve, rather crushed, seems to have been less con- 

 tracted at the antei'O-ventral margin. 



The anterior or ocular tubercle is distinct in figs. 1 and 2, more 

 prominent in a larger specimen, and less prominent in some other 

 specimens; behind it is a sulcus, forking downwards; its hinder side 

 is swollen in some degree, and between the fork is the relatively large, 

 oval, convex muscle-spot. In some cases this shows an acutely-ovate 

 area neatly reticulated (see fig. 3), and associated with a set of faint, 

 radiating, slightly tortuous, vascular lines. In one instance the reticu- 

 lation is obsolete, and the radii start from the sulcus, which is im- 

 pressed with a row of minute oblong pits (fig. 4), boj'dering the lower 

 edge of the oval tubercle. In the hollow moulds of the outside of the 

 valve this has a granulate appearance, showing that the network had 

 shallow pits between the meshes. 



A somewhat similar sculpturing is figured by Dr. F. Schmidt, for 

 Leperditia grandis, Schrenk, in his Memoir on Silurian Leperditm 

 (" Mem. Acad. Imp. Sci. St.-Petersbourg," ser. 7, vol. XXI, No. 2, 1873, 

 pp. 10-12, figs. 3, 5 and 6, and by Barrande for his Isochilina (Leper- 

 ditia) formosa, " Syst. Silur. Boheme," vol. I, Supplem, p. 534, pi. 

 xxxiv, figs. 1-3, and Isochilina (Leverd.) gigantea, ^^ op. cit., p. 535, pi. 

 xxxiv, figs. 4-6. 



Of F Schmidt's figures of X. grmdis (loc. cit.), fig. 5 is the most like 

 our figs. 1 and 2, but there are characteristic differences in outline and 

 contour. 



Although no doubt exists of these valves (figs. 1-4), being of the 

 same species with that figured and described by me in 1856, yet there 

 is a slight variance. 1st. In outline, the specimen from Eupert's Land 

 being rather more oblique by the downward and backward extension 

 of the postero-ventral region. 2nd. In the ocular tubercle being 

 stronger and more isolated in fig. 14 (1856) than even in fig. 2. 3rd. 

 In the presence of a slight oblique furrow passing from the hinder 

 edge of the sulcus to the middle of the posterior border. 4th. In the 

 marginal rim not being so broad as in the specimens now figured. 

 Hence it will be right to treat these latter as representing a variety, 

 which may be called latimarginata. 



Several specimens were collected by Mr. J. B. Tyrrell, in 1889, in the 

 white limestone on the west side of Long Point on the east side of Lake 

 Winnipegosis (or Winpipegoos), in lat. 52^55' N. and long. 99^45' W. 



^This is intended for F. Roemer's L. gigantea, regarded by Barrande doubtfully as an 

 Isochilina, but F. Schmidt Uoc. cit.) states that Barrande's figure is not quite correctly restored, 

 and that, the right valve slightly overlapping- the left at the middle of the ventral edge, it is a 

 Leperditia, and the same as Schrenk's L. grandis. 



