74 PALEONTOLOGY OF NEW YORK. 



PtERINUPECTEN (AvICULOPECTEN ?) STRICTUS. 

 ri.ATK XXIV, FIG J; ami J'LATK I.XX.XI, KIG. 18. 



PlirhD'jKittii flriilu-i. Uai.i.. Piil. N. V., vol. v. jit. 1. Pliites anil Exiilamitioiis : PI. 24, tifj. 2. Jan., 1883. 



SiiKi.i. of nu'diuin size, transversely semi-elliptiral. not olilifnic; body of the 

 shell ovate, length one-sixth less than tlie lieight ; aiiteiior and lia.sal 

 margins rounded ; posterior margin straight. 



Left valve moderately convex. Right valve tlat. 



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

 the transverse axis. 



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

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

 tending an acute angle. 



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

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

 defined by a well-marked gi'oove or sulcus; margin rounded; extremity 

 acute. Bj'Sfial siiuis distinct in the left valve, and a deep rounded notch in 

 the right valve. 



Test of left valve marked by alternating stronger and liner 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, nnich subdued on the right valve, and obsolete upon the 

 umbo. 



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 

 25.5 mm. 



This species is donlitlully arranged with the present group of I'onns. In 

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

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

 Aviculopecten, but the extent of the hinge-line, and the undefined limitation 



