332 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 45. 



PAL^OPECTEN COBSCOOKI, new species. 



Plate 29, fig. 13. 

 Cf. Avicula danbyi M'Coy (part), Brit. Pal. Fos., 1855, pi. II, fig. 12. 



Shell suborbicular, erect, inequilateral but nearly symmetrical, 

 posterior margin and wing extends backward about one-fifth more 

 than the anterior ear and margin protrude forward of a line drawn 

 vertical through the beak; left valve gently convex, beak elevated 

 but not conspicuous; right valve unknown but presumably flattened 

 or concave. The anterior ear small, flattened, angular and without 

 evident byssal sinus; margin below it slightly incurved posterior; wing, 

 triangular, flat, acutely pointed, a broad incurve connecting it with 

 the protruding lower half of margin. Surface marked by fine, sharp, 

 threadlike concentric lines and coarser ill-defined concentric wrinkles, 

 crossed by 12 to 14 obtuse radiating ridges separated by flattened 

 spaces which broaden toward the front and between them occasional 

 secondary smaller ridges. These radii are distinct over the beak and 

 central part of the shell and become faint on sides and front. The 

 hinge margin is flattened and is marked by fine longitudinal ligamental 

 striae; under the beak is a distinct small cartilage pit. On the inside 

 of the left valve each, side the beak is a strong diverging crural ridge, 

 extending 5 to 8 millimeters from the tip of beak and terminating 

 abruptly; angle of divergence about 100°. 



No evidence of either muscular scars or palhal line have been dis- 

 covered. All the specimens seen of this species are left valves. The 

 form of the right valve is inferred from a specimen of another species 

 from the same locality, showing both valves attached. Dimensions 

 of the type-specimen are as follows, namely: Length of cardinal 

 area, 37 mm.; transverse diameter across widest part, 53|^ mm.; 

 height from base to end of beak, 52 mm. ; from center of beak to tip 

 of posterior wing, 22|- mm.; crural ridges, anterior, 5^ mm.; poste- 

 rior, 9 mm. 



This species resembles M'Coy's figure 12 of Avicula danbyi, but it is 

 more erect, more nearly symmetrical, and less produced posteriorly, 

 although a larger shell, and the ear and wing are larger proportionate 

 to the size of the body part of the shell. 



Formation and locality. — In tough gray sandy shales of the Edmunds 

 formation on the east shore of Cobscook River, on outer side of the 

 southern point forming the inclosure of Carrying Place Cove in the 

 town of Trescott (locality 5.52.9A), Eastport quadrangle, Maine. 



Holotype.—Csit. No. 58953, U.S.N.M. 



PAL.S;OPECTEN DANBYI (M'Coy) (sensu stricto Williams). 



Avicula? danbyi M'Coy, Ann. Nat. Hist., ser. 2, vol. 7, 1851, p. 59. 

 Avicula danbyi M'Coy, Brit. Pal. Foss., 1855, p. 258, pi. 11, figs. 11 and 13. 



In revising this species it has seemed to the writer that M'Coy had 

 before him when writing his description three forms which may be 

 specifically differentiated. M'Coy evidently wrote the description 



