wHiTEAvEs.] LAKAJHE AXD CRETACEOUS IXYERTEBRATA. 35 



Gervillia recta, Meek and Havden. 



-Gtrvinia recta, Meek and Hayden. 1S61. Proc. Ac. Xat. Sc, Phil., vol. XIII, 

 p. -Ul. 

 " :Me6k. 1$76. Eep. r..S. Geol. Surv. Terr., vol. IX, p. 66, pi. 29, 

 flgs. 1 a, b. 



Bull's Head, about twentv-two miles west of the west end of the 

 <ryi>i-ess Hills, E. G. ^McConnell, 1S83 : one nearly jjerfect and veiy 

 typical specimen, with fragments of others in the same hand speci- 

 men of rock. 



Gervillia recta, var. borealis. (Var. nov.) 



Plate 4, figs. 2, 2 a and 2 b. 



Shell large and thick, attaining to a length of fully six inches, ine- 

 ^uivalve, the left valve being usually compressed convex and obliquely 

 flattened posteriorly and immediately under the posterior wing, but 

 rarely rather strongly convex, while the right valve is uniformly 

 almost flat : lateral margins of the valves not distinctly tortuous. 



Main body of the shell, exclusive of the posterior wing or alation, 

 elongated and narrow, about three times as long as high, very 

 obliquely sublanceolate or semi-lanceolate in outline, its upper boun- 

 dary, under the posterior alation, being nearly straight, and its lower 

 margin very broadly and convexly arched : posterior extremity 

 generally subtruncated almost vertically. Including the posterior 

 alation, the maximum height is nearly equal to one-half the entire 

 length. Posterior wing large and long, occupying more than one-half 

 the entire length, its posterior margin obliquely and conbavely emar- 

 ginate : anterior wing almost obsolete, small, angular and pointed in 

 front. Hinge-line long and straight, between one-half and two-thirds 

 the entire length in the largest specimens : beaks minute and incon- 

 spicuous, anterior but not quite terminal. 



Surface marked with a few, irregularly disposed, concentric lines of 

 growth. Cartilage pits apparently six, the three anterior ones separ- 

 ated by intervals of about equal breadth with themselves, the three 

 posterior ones much more distantly disposed. 



Muscular scars very faintly impressed and not perceptibly excavated. 

 Posterior muscular scars very large, elongated in a direction nearly 

 parallel with the longer axis of the valves, narrowly ovate, acutely 

 pointed above and narrowly rounded below, their pointed extremities 



