JONE8.] PALiltlOZOIO OSTllACODA. 63 



ostmcods and other small fossils having disappeared, leaving the 

 (juartz grains ti'anslucont and the cement yellowish. The pyrites is 

 partially decom[)osed here and there, and gives the usual taste of sul- 

 ])hate of iron. Some of the little ostracodous bodies appear of different 

 sha})es, on account of ditfereiit degi'ees of imbedraent. Some minute 

 I'ound bodies are probably other organisms. 



The valves of the suboviform specimens show no evidence ofovei-lap 

 at their mai-gins, even in natural sections ; nor are there any real 

 structui-al marks, either ocular oi* muscular, though occasional adhe- 

 sions or abrasions give those appearances. 



1 name it after J. B. Tyrrell, 1%., M.A., B. Sc, F.G.S., of the Geolo- 

 gical Survey of (^anada, who collected it at Black Island,* Lake Win- 

 nipeg. 



3. Primitia Looani, Jones. 



Ikyrichia Logani, Jones. Ann. Mag. Nat. Hist, ser. 3, vol. I, 1858, p. 244, 



pi. ix, fi^s. ()-10 (including varieties); Geol. Surv. 



Canada, Org. Remains, Decade III, 1858, p. 91, pi. xi, 



figs. 1-5 (including varieties). 

 Primiiia Logani, Jones and lloll. A. M. N. H., ser. 3, vol. XVI, 18()5, p. 417. 

 Primitia Logani, Jones. Proceed. Geol. Assoc, Pal. Biv. Entom., 1869, p. l'>, figs. 



;> and 4 (two varieties.) 

 Primitia mundula, var. ; P. mundula {?) ; and Primitia, sp., Jones. Quart. Journ. 



Geol. Soc, vol. XLVI, 1890, p. 553. 



This Primitia has characteristically a straight dorsal line, with tlio 

 terminal angles J'ecognizable, but not very strong; a convex ventral 

 maigin, often conti acted in the antei-o-ventral region, so as to make 

 the front moiety of the valves narrower (lower) than the hinder part, 

 see Decade III, pi. xi, fig. 4 and especially lig. 5 (var. leperditioides) . 

 in some instances the cuive of the ventral mai-gin is vGvy full (Decade 

 III, pi. xi, fig. 1, var. reniforrnis, and fig. 2) ; in others (as in fig. 3) the 

 ventral maigin is neai-ly straight, and the valves are much like those 

 of a long F. mundula. The surface is somewhat depressed, sometimes 

 smooth, often punctate, and always impressed with the mid-dorsal fur- 

 I'ow 01- short sulcus. 



Pnmi ^^V^' corres])()iiding to P. Loyatii, with contracted antero-ventral 

 region, as represented by fig 9, pi. v, and fig. 4, pi. xi, that is, more 

 boat-shaped than oblong, occur in the Ohazy shales (dark coloured, 



* Soe " Summary Report of the Geo logical Survey Department for the year 1890," 8vo Ottawa, 

 1891, I). 25. The fossiliferous rook referred to above belongs to tho " considerable thickness of 

 soft Pahoozoic sandstone-', apparently of the age of the Chazy (St. Peter's Sandstone) of Minne- 

 sota, which at tho southwest end of tie Island are found to run up comformably into the 

 Trenton Limestone" Hoc. cit.). 



