305 



Distinguishing ( 'ha meters. — Rhoin- 

 boidal outline; straight upper and lower 

 margin; obliquely rounded ends; flat- 

 tish surface; numerous strong, longi- 

 tudinal, inosculating, raised striae, or 

 thin wrinkles with a, tendency to be- 

 come concentric. 



Found at "Eighteen Mile Creek, Lake ftoidea. .Utenu and edge 



~ views of a left valve, x 85 



Erie Shore, N. Y." (Jones.) < after Jones) - 



Fig. 244. Entomis rhom- 



Genus STREPULA. Jones and Holl. 



[Ety. : Dimin. of Strepa, a stirrup, loop-like pattern of ridges.] 

 (1886: Ann. and Mag. Nat. Hist., Ser. V., Vol. XVII., p. 403.) 



Carapace with slightly convex valves, sub-oblong with 

 rounded unequally curved ends. Surface with narrow con- 

 centric or irregular ridges running into the slightly thickened 

 dorsal margin. The intervening furrows form broad valleys, 

 and a sub-central tubercle, or even a lobular swelling, is 

 sometimes present. The chief ridge is a free supra-marginal 

 lamina, standing outwards and downwards, and hiding the 

 real marginal edge in a side view. Edge view narrow ovate, 

 cross-barred at the sides into straight and parallel, and 

 oblique and divergent ridges. 



Strepula sigmoidalis. Jones. (Fig. 245.) (1890: 

 Quart. Journ. Geol. Soc, Vol. XLYL, 

 p. 11.) 



Distinguishing Ch aracte r s. — Acute, 

 sub-ovate outline, with straight hinge 

 line; sharp anterior an<,l rounded pos- 

 terior end; sharp ridge bifurcating forward, the upper 

 branch forming a sigmoid flexure. 



Found in the "Hamilton group, at Eighteen Mile Creek, 

 Lake Erie Shore, N. Y." (Jones.) 



Strepula plantaris. Jones. (Fig. 246.) (Quart. 

 Journ. Geol. Soc, Vol. XLYL, p. 540, PI. XY.) 



Fig. 245. Strepula Isig- 

 moidalis. Left valve, x 25 

 (after Jones) . 



