302 Professor Rupert Jones — Isochilinm from N. America. 



smoothed ; and the other presents a broken surface, showing one 

 good Ostracod valve, like that of No. 1, but smaller, together with 

 two still smaller, but allied, specimens, and some indeterminable 

 fragments. 



Smaller than Fig. 1, and of similar outline, but with less 

 protrusive postero-ventral curvature, and more convexity in the 

 posterior moiety of the surface of the valve. Differences in the 

 superficial convexity of Isochilince are shown in figs. 1-6 of 

 Professor Whitfield's pi. xiii, 1889. 



The tubercular border of the nuchal notch partly remains, one 

 tubercle on one side and two on the other. 



Length 8 mm., height 5 mm. In specimen No. 2, ' Bala Drift,' 

 Hamilton, Ontario. 



II. Isochilina gregaria (Whitfield), var. (?). 



Small bivalved carapace, much like Nos. I and la in shape, 

 subovate, convex in the middle of the valve. 



Length 3|- mm., height 2 mm. 



III. Isochilina, sp. ? (Fig- 3.) 



No. 3 is a limestone similar to that of No. 2, but coarser and 

 evidently full of organic fragments. One surface is flat and smooth, 

 probably the natural surface of a glaciated rock. The other face 

 exhibits an internal cast of an Ostracod valve, probably an Isochilina, 

 somewhat distorted by pressure. Among the accompanying obscure 

 little organisms is a small Beyrichia (?) or Tetradella. 



This cast of a somewhat crushed valve is larger than either 

 Nos. I or la ; suboblong, with marginal rim ; surface somewhat 

 undulating, having been distorted by pressure. Depressed across 

 the hinder moiety of the valve with a gentle curve. An obscure 

 indication of the base of a broken spine near the posterior margin. 



Length 10mm., height 7mm. 'Bala Drift,' Lake Shore, Winona, 

 Ontario. 



IV. Tetradella (?), sp. 



The little Beyrichian (?) individual (length 2 mm., height l^mm.) 

 on the specimen No. 3, ' Bala Drift,' Lake Shore, Winona, Ontario, 

 with its narrow lobes, although obscure, bears evidence of having 

 a long semicircular thin ridge along the ventral region, just within 

 the ventral border, giving rise apparently to three ridges stretching 

 across the central area towards the dorsal edge. This form may be 

 said to be allied to Beyrichia Marchica, Krause,^ and Beyrichia 

 Busseacensis, Jones,^ and more particularly to E. 0. Ulrich's 

 Tetradella siihquadrata, Journ. Cincin. Soc. Nat. Hist., vol. xiii, 

 pt. 1 (1890), p. 115, fig. 2. All of them belong to the Lower 

 Silurian series. 



Some Lower Silurian (probably Chazy) specimens from Ottawa 

 (Ontario), Canada, were referred to in the Quart. Journ. Geol. Soc, 



1 Zeit. d. D. Geol. Ges., 1889, p. 19, pi. ii, figs. 9-11. 



2 Quart. Journ. Geol. Soc, toI. ix (1853), p. 160, pi. vii, figs. 5 and 6 ; and 

 Eiv. Entom. Geol. Assoc, 1869, p. 15, figs. 23a-b. 



