LAMELLIBRANCHIATA. 53 



LiTRIOPEI I'I.n LNOM1 BFOBHI8. 



I'l.ATK H. Hi, M.I'I.ITI \ I I . im, I'HII I \\\l|. Mi.. i. 



Lyriopecten anomUtfonnig, Hall. MS8. Cur vol. v. pt. I. i s 77. 



Catalogue amer, PaUeozoic Fossils, 8. a. Mn.in 1877. 

 Pal. N. Y.. vol. \. pt. l. Plates and Explanations: PI. •). fig. 10; pL 10, 

 Bg. 5. Jan., 1888. 



Shell larger than medium size, obliquely elliptical or obovate ; heighl nearh 

 equal to the length ; the transverse axis makes an angle <>f about 15 with 

 the hinge-line; margins regularly rounded anteriorly anil along the base, 

 becoming obscurely truncated on the upper postero-lateral portion of the 

 shell. 



I.i It valve slightly convex. Right 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 

 anterior 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 ri^ht valve a very deep, elliptical sinus. 



Teat 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 stria? of growth ; the larger rays are aboul 20 in 

 number. <>n the right valve the radii are represented l>\ obscure, undu- 

 lating, unequal stria?. The ears show the same surface markings. 



Cartilage-pit small. Ligamental area thickened, with about eight flat, 

 longitudinal lines extending to the extremities of the hin§ 



A left valve measure-- 62 mm. from the anterior ear to the postero-basal 

 margin; from the extremity of the beak the height i- 55 mm., ami the 

 length, parallel to the hinge, is aboul •">! mm.; hinge-line 27 mm. 



