41 



S. ANTIQUATA, Sowerby.— Prinsta Bay and East Point; Divs. 2, 3, A. 

 G. 



S. PLANUMBONA, Hall.— Junction Cliff; Div. 1, A. G. Also in H. K. 

 Genus Leptaena, Dalman. 



S. SERICEA, Sowerby, — Very abundant and in a fine state of preser- 

 vation at Gamache Bay ; Div. 1, A. G. Also at numerous localities in 

 the underlying H. R. 



L. TRANSVERSALis, Dalman. — Four miles west of Jupiter River, East 

 Point and the Jumpers ; Div. 2, 3, 4, A. G. 



Genus Orthis, Dalman. 



0. PORCATA, McCoy. — Abundant at Gamache Bay ; Div. 1, A. G. This 

 species also abounds in the Trenton limestone at the City of Ottawa. 



0. Davidsoni, De Verneuil. — Abundant at the Jumpers and other loca- 

 lities in Div. 4, A. G. 



0. LYNX, Eichwald. — Abundant at Gamache Bay ; Div. 1, A. G. Also 

 in H. R. 



O, Laurentina, B., Rep. 1857, p. 297 Abundant at Gamache Bay; 



Div. 1, A. G. 



O. Maria, B.,Pal Foss., vol. i, p. 137. — Gamache Bay ; Div. 1, A. G. 



0. parva ? Pander. — A species agreeing very nearly with the figures 

 and descriptions of De Verneuil, Pal. Russ., occurs at Junction Cliff, 

 Gamache Bay, the Jumpers and other localities in Divs. 1, 4. 



0. media, Shaler. — The following is Mr. Shaler's description of this 

 species. Bui. M. C. Z., p. 65. 



" Shell orbicular ; hinge-line one half less than width of shell. Toothed 

 valve evenly convex ; depth, in adult specimens about one fourth the 

 height, in young specimens proportionately a httle greater ; umbo slightly 

 elevated, rising above the hinge line one eighth the distance from beak to 

 border, slightly compressed, occupying at the hinge-line about one fourth 

 the diameter of the valve ; beak small, distinct, slightly recurved, a little 

 overhanging the area ; area small, rather broad. Fissure triangular, one 

 third as wide as length of hinge-line. Socket valve transversely flattened, 

 a slight mesial depression dividing the surface into two lobations. ■ 



" Differs from its European representatives, being more orbicular, having 

 less projecting umbo, less incurvation of beak, much finer radial striae, 

 closer approximation of the brachial supports of the socket-value, and less 

 length of the adductor impressions in the same valve." 



