76 PALEONTOLOGY OF NEW YORK. 



PtERINOPECTEN DISPANDUS, 11. sp. 

 PLATK I.XXXII. FIGS. II, li. 



.SiiKi.i. large, soiiK'wliat liitiinlMpiil-ovatt', i)lilii[iit', varviiij;' with iIr' at;v of the 

 slioll ; length a little greater than the height; margins regularly curved, 

 extending behind. 



Left valve convex. Right vahe depressed-convex, somewhat smaller 

 than the left, and proportionally longer. 



Hinge-line straight, less than the greatest length of the slicll, nearly 

 central. 



Beaks oljtnse, little elevated, anterior to the middle, directed forward. 

 Umbonal region scarcely defined, moderately prominent, subtending a right 

 angle. 



Ears triangidar, nndefined; margins concave. Posterior ear larger than 

 the anterior. Anteiior cai- liuiited by an undefined sulcus and moderate 

 sinus; extremity rounded. In the right valve, the anterior ear is narrow, 

 acute, with a deep, angular byssal sinus. 



Surface ornamented by prominent, r()\inded radii, which alternate irregu- 

 larly with finer intercalated radii, and increase in size and number towards 

 the margin ; crossed by concentric striae, with more distant varices of growth 

 which crenulate the radii. The rays are stronger over the anterior slopes, 

 and are continueil on the ears, somewhat finer on the posterior and stronger 

 on the anterior. In the right valve the strong rays are regularly duplicat- 

 ing, and are finer and equal on the posterior ear, with a few stronger ones 

 on the anterior ear. 



Ligamental area narrow. 



Two left valves measure respectively 45 and 87 mm. in length, 42 and 

 44 mm. in height, hinge-line 40 and .'id iniu. A right valve is 82 mm. in 

 length, 27 mm. in height, liinge-line 28 mm. Other specimens of the left 

 valve vary considerably, apparently according to age. 



This species differs from P. Vertumnus in its greater proportional height, 

 shorter hinge-line, abruptly rounded radii, and niuidi sharper small intermediate 



