LAMELLIBKANCHIATA OP THE LOWER :MA1;LS. 73 



Mr. Meek lias refei-red to this shell on page 35, in his Invert. Pal. U. S. 

 Geol. Surv. Territ, where he speaks of it as being evidently an Oxytoma, 

 a genus founded on a Jurassic shell of very different characters from this 

 one. (See Oxytoma mucronata, Pal. Black Hills, p. 357, pi. iv, figs. 1 and 2, 

 which is the species on which the genus Oxytoma was founded.) 



Form.ation and locality. — In the Lower Green Mai-ls of the Cretaceous at 

 Freehold, New Jersey. The specimens were collected and kindly loaned 

 for use by Miss F. M. Hitchcock, of New York City. 



GERVILLIOPSIS, u. g. 



Shell bivalve, resembling GervilUa in form, but with the anterior end 

 squarely truncate and the beaks terminal. Hinge with a broad ligamental 

 area, crossed on the posterior side by vertical cartilage pits and fine, oblique 

 corrugations instead of teeth. Area continued down the anterior truncation 

 as in Myalina, but deeply and abruptly excavated, forming a gaping anterior 

 end. A large ovate muscular scar occurs, subcentrally situated, just within 

 the extremity of the hinge, and a smaller double one obliquely placed 

 between it and the anterior end. Small scars also occur beneath the hinge 

 Shell pearly and iridescent. 



This genus of shells difi^ers from GervilUa, under which it has hereto- 

 fore been classed, in the absence of the teeth on the posterior portion of 

 the hinge, and the oblique tooth-like ridges below the ligamental area on 

 the posterior end. It also differs in the truncation of the anterior end or 

 wing; in the continuation of the ligamental or striated area-like surface 

 along the anterior truncation, and in the gaping of the valves anteriorly. 

 In the last two features it appears to combine features of the genus Myalina 

 while in general form and in the ligamental area and cartilage pits of the 

 posterior hinge it resembles GervilUa. Type GervilUa ensiformis Conrad. 



Geological position. — As yet known onl}^ by two species, from the lower 

 bed of the Lower Green Marls of the Cretaceous of New Jersey. 



Gervilliopis eusiformis. 

 Plate XV, Figs. 8-11, .ami Plate XVI, Fig. 5. 

 GervilUa ensiformis Courad. Jour. A. iST. Sci., Vol. Ill, p. 328, PI. XXXIX, Fig. 10. 



Shell of moderately large size and thickened, falciform, very oblique; 

 the body of the shell finally becoming parallel to the hinge or even slightly 



