NATURAL SCIENCES OF PHILADELPHIA. 1'J 



AVICULOPECTEN SPINDLIFERUS, M. and \\\ 



Shell of medium size, rather compressed, having a moderately oblique 

 truncato-suboval, or suborbicular outline. Hinge apparently nearlj equal- 

 ing the antero-posterior diameter of the shell; ventral margin forming a 

 broad seiniovate outline, being more abruptly rounded up behind than in 

 front. Posterior wing rather pointed, apparently not quite as long as the 

 rounded margin of the valves below, from which it is separated by a round* I 

 sinus. Anterior wing compressed, narrow, as long as the anterior margin of 

 the valves; in the left valve pointed, and separated from the margin below by 

 a narrowly rounded, rather deep sinus. Beak of the left valve moderately 

 prominent, and placed a little in advance of the middle. Surface of same 

 valve ornamented with numerous, distinct, unequal, radiating costs, arranged 

 usually with one or two smaller ones between each two of a somewhat larger 

 series, the latter of which bear numerous little round, regularly arranged, 

 somewhat oblique spines ; crossing the whole there are also numerous minute 

 concentric striae. (Right valve unknown.) 



Height of left valve, about 1-50 inch ; antero-posterior diameter, near 2 

 inches. 



This is a delicate species, apparently with thin valves. Its costaa seem to 

 be nearly equally developed over the whole of the left valve, including the 

 wings, or at any rate the posterior one. On the body of this valve, near the 

 ventral margin, about five of the larger spiniferous costs, and some Bis 

 or eight of the smaller non-spiniferous ones may be counted in the space 

 of half an inch. The spines of the larger costae were short, round and 

 pointed (not being formed by vaulted laminae of growth), and arranged 

 along these costae at regular intervals of about 0-10 inch apart, those at the 

 ventral margin being larger than the others, and projecting a little below the 

 border. An impression of a part of the anterior wing of the right valve shows 

 that it was distinctly costate, two or three of the costae running nearly paral- 

 lel to the hinge margin, and bearing short spinules. 



In casts of this species without the spines, the costae present much the same 

 subnodose appearance as those seen on A. fa llax (= Peclen fallax, McCoy, 

 Carb. Foss. Ireland, pi. 14, fig. 2), but that species seems to have had uo 

 spines. It is also much less oblique, and higher in proportion to its antero- 

 posterior diameter. 



We place this species in the genus Aviculopecten only provisionally, as we 

 have not seen its hinge. It is highly probable that there are a number of un- 

 described genera among the Palaeozoic species usually included in the genus 

 Aviculopecten, or wrongly referred by some to the genus Pecten. 



Locality and position. Crawfordsville, Indiana. Keokuk division of the 

 Lower Carboniferous series. 



Genus CARBONARCA, Meek and Worthen. 



Shell (as determined from internal casts) equivalve, inequilateral, very 

 convex, transversely oblong or oval; umbones gibbous, prominent, and 

 strongly incurved with subangular or prominent posterior slopes; valves 

 ' closed all around, with smooth margins; ligament external; cardinal margin 



- ob- 



a little arched, with, at the anterior extremity in each valve, two rather 

 lique comparatively stout teeth, and extending along its entire length I 

 immediately behind these, a row of minute interlocking teeth or crenulati 



rom 

 ations, 



itely 

 as in Area. _ _. ,._. , 



This genus seems to belong to the Areidse, near Isoarca. It differs, how- 

 ever, very decidedly from that genus, in having, in addition to the ' ^" 

 terl 

 ope 



locking emulations along the whole length of the hinge, two well level- 

 ed and independent larger teeth at the anterior end oi the hinge. The 

 specimens seen are all internal casts, but an impression o the hinge of a 

 right valve, in the matrix, shows its characters very clearly. There j s no 



1870.] 



