5(J PALAEONTOLOGY OF THE UPPER MISSOURI. 



Subfamily MELINLN"^. (See page 28.) 

 Genus BAKEVELLIA, King. 



Synon.—Afytilites (sp.), Schlot. Akad. Munch. VI, 1816, 30 ; ib. Petre/. 1820, 293. 



Amciila (sp.), J. dk C. Sowerby, Trans. Geol. Soc. 2d ser. Ill, 1829, 119.— Goldf. Petref. 2d part, 1826, 

 126, and of several others (not [Klein] Lamk.). 



Bakevellia, King, Catalogue, 1848, 10. 



Gervillia, Geinitz, Versteineruugen, 1848, 10; ib. Dyas, 1862 (not Defrance, 1820). 

 Elytn. — Dedicated to Robert Bakewell, of Hampstead, England. 

 Type. — Avicula antiqua, Munster. 



Shell more or less aviculiform, subequivalve ; valves somewhat sinuous and a little 

 gaping in front for the passage of the byssus. Umbpnes depressed and oblique. 

 Surface with concentric striae. Hinge provided with a few linear anterior and 

 posterior lateral teeth, arranged nearly or quite parallel to the cardinal margin. 

 Muscular scars much as in Pteria (Avicula)^ excepting that the anterior one is 

 larger and more distinct. Cardinal area usually well developed in both valves ; 

 cartilage furrows distinct, two to five in each valve. 



Animal unknown. 



In form, as well as in the possession of a more or less developed anterior and 

 posterior wing, and the inequality of the valves, the species of this genus are often 

 very similar to Pteria ; from which, however, they differ in the possession of a 

 large, deeply grooved cardinal area, and a divided cartilage, as well as in the 

 nature of the hinge teeth, and the proportionally larger size of the anterior muscu- 

 lar impression. 



In the possession of a broad cardinal area, crossed by a few deep furrows for the 

 reception of the cartilage, the Bakevellias seem to present affinities to the genus 

 Gervillia, which some of the species closely resemble in form. The nature of the 

 hinge, however, and the greater development of the anterior muscidar scar, clearly 

 separate them from that group, at least generically. 



Prof. King, the able author of the excellent Monograph of the Permian Fossils 

 of England, thinks the comparatively large size of the anterior muscular impression 

 in this genus, sufficiently marked, not only to separate it from Pteria, but to remove 

 it entirely from the Pteriida;. Still in the rather low, or nearly sub-central position 

 of the posterior muscular impression, when taken in connection with the general 

 similarity of these shells to Pteria and Gervillia, they seem to present a combina- 

 tion of characters bringing them very near, if not within the Pteriida^. 



In Europe, the genus Balcevellia is generally regarded as being restricted to the 

 Permian System. If the following described species, however, really belongs to 

 this genus, it woiUd seem to have been introduced at a somewhat earlier period 

 here, since we have seen it in Kansas in beds we regard as probably of the age of 

 the Coal Measures, though it ranges up, and is most abimdant in the Permian beds 

 above. 



