7 1 l>AL;EO\TOLOGY OF NEW YORK. 



Pterinopectbs (AviCULOPECTKN I) STIUCTUS. 



PLATE XXIV, FIG. •-': ami PLATE I. XXXI, FIG. 18. 



Pttrinopecten strictus, Bah. PaL N. Y., vol. v, pt. 1. Plates and Explanations : PI. 24, ti^. 2. Jan., 1883. 



Sin. i.i. of medium Bize, transversely Bemi-elliptical, not oblique ; body of the 

 shell ovate, length one-sixth less than the height; anterior and basal 

 margins rounded ; posterior margin straight. 



Left valve moderately convex. Right valve flat, 



Hinge-line straight, equal to the length of the shell, central as regards 

 the transverse axis. 



Beaks obtuse, low, directed slightly forward, anterior to the middle of the 

 hinge-line. Umbonal region moderately prominent in the upper part, sub- 

 tending an acute angle. 



Ears triangular. Posterior ear much the larger, flat ; margin concave; 

 extremity sbghtly acute, obscurely defined. Anterior ear small, convex, 

 defined by a well-marked groove or sulcus; margin rounded; extremity 

 acute. Bvssal sinus distinct in the left valve, and a deep rounded notch in 

 the right valve. 



Test of left valve marked by alternating stronger and finer rounded radii, 

 crossed by sharp, elevated, concentric lines of growth and more distant 

 undulations, with imbricating lamellose lines. These markings are continued 

 over the ears, much subdued on the right valve, and obsolete upon the 

 undio. 



Ligamental area marked by two or three furrows, and a central cartilage- 

 pit. 



The specimen figured has a length of 25 mm., height 30 mm., hinge-line 

 "J •">.") mm. 



This species is doubtfully arranged with the present group of forms. In 

 some aspects it resembles P. conspectus, but is specifically very distinct. It 

 might be compared with the young of some large forms of Lyriopecten or with 

 Aviccloi'kcten, but the extent of the hinge-line, and the undefined limitation 



