WAVERLY GEOUP SPECIES. 295 



Genus AVICULOPECTEI^, McCoy, 1851. 



(An. aud Mag. N. H., VII., 171.) 

 AVICULOPECTEN CRENISTRIATUS, Meek. 



Plate 15, figs. 7a, b. 

 Aviculopecten crenistria, Meek (1871) ; Proceed. Acad. Nat. Sci., Philad., XXIII., 4. 



Shell thin, attaining a moderately large size, plano-convex, with a 

 truncato-suborbicular outline ; heighth and breadth nearly equal ; basal 

 margin more or less regularly rounded ; posterior margin rounding from 

 the posterior ear into the base, sometimes a little straightened above ; 

 anterior side rounded so as to make a shorter curve than the other; 

 hinge less than the breadth of the valves in length, but rather long. 

 Left valve moderately convex ; beak rising a little above the hinge mar- 

 gin, nearly or quite central, and not oblique ; posterior ear small, with a 

 marginal ridge, flat, without being separated from the swell of the umbo 

 by a sulcus, rather acutely angular at the extremity, and distinctly 

 shorter than the margin below, from which it is separated by a nearly 

 rectangular notch ; anterior ear larger, or sometimes nearly as long as 

 the margin below, rather acutely angular at the extremity, convex, and 

 separated by a rounded impression from the umbo, defined by a rather 

 deep subangular marginal sinus. Surface ornamented by numerous, very 

 slender, radiating costae or raised lines, separated by rather wide, flat 

 spaces, in each of which a still smaller line is sometimes intercalated ; 

 crossing all of these are smaller, regularly arranged, sharply elevated, 

 concentric lines, that seem to form little projections at the points of 

 crossing, so as to give a rough appearance to the surface; costce becoming 

 more closely crowded, but not smaller on the ears. Right valve flat or a 

 little concave, with beak obsolete ; ears flat, and of nearly the same size 

 and form as in the other valve, excepting that the anterior one is broader 

 and defined by a more shallow and more rounded sinus than appears to 

 exist in the left valve; surface cancellated by regular, rather closely 

 arranged, radiating and concentric lines, the latter being very sharply ele- 

 vated, and minutely and regularly waved, crenate, or somewhat vaulted; 

 radiating costse somewhat larger and more distant on the ears. 



Height, 2.50 inches ; breadth, 2.78 inches ; convexity, 0.40 inch. 



The specimens of this species are not very well preserved, being 

 mainly casts with some portions of the surface. It is rather remarkable 

 in having only a comparatively shallow rounded sinus under the an- 



