Lamelljbranchiata. 255 



two sharp or rounded rays, crossed by very fine, sharp, concentric 

 striae. The radii gradually diminish in strength toward the ears, 

 where they are represented by elevated, narrow lines. Ligamental 

 area marked by several logitudinal striae. 



The height of the specimen is 97 mm., length 104 mm., hinge- 

 line 44 mm. Three of the stronger rays occupy a space of 12 mm. 

 at the basal margin. 



The specimen described is the impression of the exterior of a left 

 valve ; it is quite characteristic and very distinct from other known 

 species in its form and surface markings. In ornamentation and 

 general outline there is some resemblance between this shell and L. 

 macrodontus, but it is less convex, the rays are more elevated, and 

 more sharply defined. The geological horizons of the two species are 

 also widely separated. 



Formation and locality. In coarse, arenaceous slates of the Upper 

 Chemung group, at Montrose, Susquehanna county, Penn. 



LYEIOPECTEN ANOMICEFORMIS. 



Lyriopecten anomwformis, Hall. MS. for vol. v, pt. 1. 1877. 



Lyriopecten anomiceformis, Hall. S. A. Miller. Cat. Amer. Pal. Foss. 



1877. 

 Lyriopecten anomiceformis, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Ex- 

 planations : PI. 4, fig. 10 ; pi. 10, fig. 5. Jan., 1883. 



Shell larger than medium size, obliquely elliptical or obovate ; height 

 nearly equal to the length ; the transverse axis makes an angle of 

 about 45° with the hinge-line; margins regularly rounded ante- 

 riorly and along the base, becoming obscurely truncated on the 

 upper postero-lateral portion of the shell. Left valve slightly con- 

 vex. Eight valve nearly flat. Hinge-line straight, anterior ; length 

 equal to one-half the transverse diameter of the shell. Beak of 

 left valve obtuse, rounded, oblique, not well-defined, situated an- 

 terior to the middle of the hinge, and extending to the hinge- 

 margin, but not rising above it. Beak of right valve scarcely 

 defined. Anterior ear small, obscure, only indicated by the short 

 portion of the ligamental area anterior to the beak. Posterior ear 

 undefined triangular ; margin straight ; extremity obtuse. Byssal 

 sinus in the left valve a small notch ; in the right valve a very deep, 

 elliptical sinus. * 



Test thin, marked on the left valve by numerous fine, thread-like 

 radii, of which every fourth to eighth one is much stronger than the 

 intermediate lines, crossed by fine striae of growth ; the larger rays 



