1916] Packard: Mesozoic and Cenozoic Mactrinae 311 



rounded or subangular at its connection with the base below; dorsal out- 

 line sloping from the beaks in front and behind, at an angle of 120°; 

 beaks central, rather elevated, but small, and not projecting much above 

 the hinge margin; surface marked only by moderately distinct lines of 

 growth. Posterior muscular impression oval, well-defined; pallial line dis- 

 tinct, and provided with a rather deep, horizontal sinus, about one-third 

 longer than wide. The type specimen had the following dimensions: 

 length, 55 mm., height, 41 mm., convexity, 12 mm. 



The type of this species was obtained from a piece of float found 

 on the shore of the Straits of Juan de Fuca. 



Occurrence. — Cretaceous (?) j Straits of Juan de Fuca (Meek). 



MACTRA(?) MONTEREY AN A Arnold 



Mactra monteryana Arnold, Proc. U. S. Nat. Mus., vol. 34, p. 381, pi. 35, fig. 

 2, 1908; U. S. Geol. Surv. folio 163, pi. 35, fig. 2, 19U9. 



Arnold described this species as follows : 



Shell attaining a length of at least 30 mm.; width a little more than one- 

 half length, subtrigonal, compressed, subequivalve, inequilateral; umbones a 

 little behind middle, small, turned slightly forward; anterior margin consid- 

 erably longer than posterior; very gently convex; anterior extremity quite 

 sharply angulated below; a faintly developed carina or angle, most promi- 

 nent near umbo, extends from the latter to the anterior extremity; base only 

 very slightly rounded; posterior dorsal margin nearly straight, sloping only 

 moderately steeply; posterior extremity regularly rounded and situated 

 nearly midway between base and umbo; surface sculptured by numerous fine 

 incremental lines and numerous obsolete short undulations. The dimensions 

 of the type are: length, 31 mm., height, 18 mm., convexity, 2 mm. 



This form has not been recognized by the writer. Its generic 

 position is uncertain, but judging from the cut and the description, 

 it is more likely to be a Spisula than a Mactra. 



This species was described from a fossil specimen obtained from 

 the Monterey shales on Love Creek, Santa Cruz County, California. 

 The type is in the United States National Museum under catalogue 

 number 165463. 



Occurrence. — Miocene : Monterey group, Santa Cruz Mountains, 

 California (Arnold). 



MACTRA (?) STANTONI Arnold 



Mactra stantoni Arnold, Proc. U. S. Nat. Mus., vol. 34, p. 357, pi. 31, fig. 3, 

 1908. 



