32 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



P tor ■ a linguiformis, E. & S. (sp.). 



Plate 10, figs. 1, a, b, c, d. 



Avicula linguiformis, Evaus and Slumlord (1854), Proceed. Acad. Nat. Sci. Philad., VII, 163. 

 Pteria linguiformis, Meek (1864), Smithsonian Check-list N. Am. Cret. Fossils, 9. 



Compare Avicula nitida, Forbes (18*46), Traus. Geol. Soc. Lond., VII, 151. — Stoliczka (1871), 



Palaeont. Indica, III, pi. xsxviii, figs. 11-12; also, A. petrosa, Conrad (1850), Jour. 



Acad. Nat. Sci. Philad., II (u. a.), pi. 24, fig. 15. 



Shell obliquely ovate-subtrigonal, or linguiform, moderately convex, and 

 not very inequivalve, both valves being convex, but the left more so than the 

 right ; hinge-line nearly equaling the greatest length in the young, but pro- 

 portionally shorter in the adult, sometimes with a narrow marginal ridge 

 posteriorly in the. right valve; posterior wing of moderate length, pointed, 

 compressed and defined by a rather deep, rounded sinuosity of the margin 

 below ; anterior wing narrow, somewhat produced, pointed, and less com- 

 pressed than the other, defined by a shallow, broad, marginal sinus that is 

 very little, if any, deeper in the right than the left valve, though in the 

 former the wing is separated from the swell of the umbo by a shallow sulcus 

 extending from the sinus directly upward to the anterior side of the beak ; 

 anterior margin sloping, with more or less convexity of outline, from the 

 sinus under the wing, obliquely backward and downward into the base, 

 which rounds backward to the narrowly -rounded posterior basal extremity; 

 posterior margin under the ear oblique, and generally more or less sinuous 

 in outline; surface smooth, or only marked by lines of growth; beaks sub- 

 equal, very oblique, depressed, and placed in advance of the middle of the 

 hinge-line. 



Length of an adult specimen, from outer end of anterior wing to 

 posterior basal extremity, 1.15 inches; length of hinge, about 0.95 inch; 

 convexity of the two valves, 0.44 inch; that of the left valve being 0.26 inch. 



This shell is evidently closely related to Avicula nitida, Forbes 

 (rr Avicula (Mdeagrind) nitida, Stoliczka), from the Cretaceous rocks of 

 Southern India, and may not be specifically distinct. Indeed, young examples 

 agree almost exactly with Dr. Stoliczka's figures of the Indian species of 

 corresponding size. His figures of the adult specimen of A. nitida, however, 

 show a much less oblique outline, and less produced wings, as well as more 

 nearly equally convex valves than in the form under consideration. The 

 absence of a pointed posterior wing, and the straightness of the posterior 

 margin of the specimen represented by his fig. 11 of pi xxxviii are probably 



