PALJEONTOLOGY OF NEW YORK. 



AVK'ULOPECTEN ClKON. 



•I.ATK I, Kl(.. 1. 



Ariculopeclm Clem, Hall. Piil. N. Y.. vul. v, jit. 1. Plates ami Kxplanatiotis : PI. 1, tig-. 1. Jan., 1883. 

 Conijiare with the joiinjf of A. primrpx. 



Shkll .^iiiiill, ovate; transverse axis slighth' oblique; length somewhat greater 

 than the lieight ; margins reguhirly romuled. 



Left valve convex, the convexity c(|ii;il to alidut one-sixtli tlic Iciiutli of 

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

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



Ilinge-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 Ijy 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 ra3's have (me or two fmri- lines 

 between. The lines of growth exti'iid uwi the ears, but less distinctly than 

 over the l)0(ly of the slicll : ami otlicrwisc 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 'JO mm. 



This form resemliles tlic young of A. princeps, l>\it it is less oMiipic. and tlie 

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

 authentic specimens. Tlie 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 

 ha.s fewer and sharper radiating stria;, and the geological horizons of the two 

 are widely separated. 



Formation and localitij. Tpper Ilelderberg limestone, Cohnnbus, Ohio. 



