306 THE CARBONIFEROUS SYSTEM. 



the plaits. The plaits in the internal cast appear nodose. The ribs 

 are visible in the cast of the interior, but less distinctly. In some 

 specimens which have the surface well preserved, the tubercles in the 

 ribs become elegant scaly processes, and in others the spaces 

 between the ribs have regular microscopic concentric lines between 

 the ribs. In others there are occasional coarse concentric ridges. 

 Though at first disposed to regard some of these varieties as distinct, 

 the comparison of a great number of specimens induces me to regard 

 them as varieties of the same species. It is allied to A. fallax., 

 M'Coy, and A. occidentalism Shumard. 



Aviculopecten reticidatus, n. sp., coll. J. W. D. (Fig. 112), Gay's 

 River. — In form and size similar to the last, but the left valve much 

 flattened, and the surface marked with numerous sub-equal ribs, crossed 

 by strong concentric stride, giving a reticulated appearance. 



Pig. 112. — Aviculopecten reticulatus ; Fig. 113. — Aviculopecten simplex. 



Sculpture magnified. -, 



(a) Sinistral, and (6) dextral valve. 



Aviculopecten simplex^ n. sp, (Fig. 1 13), coll. J. W. D., Shubenacadie 

 Windsor, etc. — Shell semi-orbicular, equivalve, very convex, the thick- 

 ness being equal to half the transverse diameter, greatest just behind 

 the middle, sloping thence with a gradual curve to the front, hinge- 

 line less than longitudinal diameter. Ears w^ell marked, anterior ones 

 abruptly flattened, that of the right valve being flatter than the 

 other, and separated from the umbo by an oblique groove. Anterior 

 ear of left valve with a shallow rounded notch ; that of the right 

 valve much deeper. The groove separating the ear from the umbo 

 is concave, narrow and shallow at first, but becomes wider and deeper 

 until it runs into the notch. The right valve has a narrow, concave, 

 triangular area. Umbones approximate, much inflated. That of left 

 valve touches and passes slightly beyond the binge-line. That of 

 the right is elevated above the hinge-line by the hinge-area. Surface 

 of valves generally smooth, ornamented by a few more or less pro- 

 minent concentric lines of growth. 



This species approaches to A. pusillus of the Permian, but differs 

 in being more tumid, more nearly circular, and having longer ears. A 

 single valve found in the Upper Coal formation limestone approaches 

 still more nearly to A. pusillus. It may represent another species, 



