PALEONTOLOGY OF NEW YORK. 



AVICULOI'ECTKX Cl.KON. 



PLATE I. Hi.. I. 



Aviculopecten Clean, Hall. Pal. N. V., vol. v. j » t . 1. Platee and Explanations : PI. 1. ti^.-. 1. Jan., 1883. 

 Compare with the young of A. prlnceps. 



Shell small, ovate: transverse axis slightly oblique; length somewhat greater 

 than the height ; margins regularly rounded. 



Left valve convex, the convexity equal to about one-sixth the length of 

 the hinge-line. The point of greatest convexity is just anterior to the 

 centre of the shell and towards the beak. Right valve not observed. 



Hinge-line straight, length five-sixths the height of the entire shell. 



Beak anterior to the middle of the hinge, not prominent. 



Ears defined by the absence of radiating lines, but not by any marked 

 change in the convexity of the shell ; lateral margins concave. The anterior 

 ear is limited by a shallow groove. The posterior ear is about twice the 

 size of the anterior. 



Test thin, ornamented by a reticulation of fine radiating lines, and finer 

 concentric* stria? of growth. The stronger rays have one or two finer lines 

 between. The lines of growth extend over the ears, but less distinctly than 

 over the body of the shell; and otherwise the ears are nearly smooth. 



Interior not observed in the specimen described. 



The length of this specimen is 21 mm., height 24 mm., hinge-line 20 mm. 



This form resembles the young of A. princeps, but it is less oblique, and the 

 ears less strongly defined than in the young of that species as represented in 

 authentic specimens. The figure does not quite represent the form of the 

 specimen, and the posterior ear is not so well defined as is shown in the 

 illustration. The form A. exacutus is very similar to this one ; but that species 

 has fewer anil sharper radiating striae, and the geological horizons of the two 

 are widely separated. 



Formation and locality. Upper Helderberg limestone, Columbus, Ohio. 



