Beede.| Carboniferous Invertebrates, 113 



ENTOLIUM. 



Meek. Geol. Surv. Cal. [I. 



Entolium aviculatum. Plate XIX. tig. 1. 



Pecten avieulatus Swallow, Trans. St. L. Acad. Sci.', i. p. 213, (1858). 

 Entolium aviculatum Meek, Fin. Rep. U. S. Geol. Surv. Neb., p. 189. pi, 

 ix. ff. lla-g, (1872). 



Meek's description : Cl Shell compressed lenticular, very thin, 

 nearly or quite equivalve, suborbicular, or broad subovate in 

 outline exclusive of the ears, the antero-posterior diameter 

 being often a little less than that at right angles to the same ; 

 sides and base more or less regularly rounded ; lateral margins 

 above the middle apparently a little gaping, straight, and con- 

 verging to the beaks at an angle of 115° to 125°; cardinal 

 margin very short, or less than one-third the transverse diam- 

 eter of the valves, and in the left valve generally concave, or 

 more or less sloping in outline from the extremities of the ears 

 to the beaks ; straight or nearly so in the right valve ; ears 

 small, flat, very nearly equal, obtusely angular at the extremi- 

 ties, and separated from the body of the valves by an impressed 

 line, not defined by any proper sinus in either valve, though 

 the broad obtuse notch separating the anterior one from the 

 straight, sloping adjacent margin is slightly more defined than 

 the other; beaks small, rather compressed, equal, and not pro- 

 jecting beyond the cardinal margin. Each valve with two 

 shallow undefined impressions diverging from the beak nearly 

 to the anterior and posterior margins ; that on the posterior 

 side being longer than the other. Surface with very fine close 

 concentric stria 4 , scarcely visible without the aid of a magnifier ; 

 crossing these arc sometimes seen traces of extremely minute 

 radiating striae, curving gracefully outward toward the lateral 

 margin-." In a foot-note he says: "In most of these speci- 

 mens these radiating stria- are entirely obsolete, even as seen 

 under a magnifier; and it is generally only on specimens that 

 have been slightly weathered that they are most distinctly seen, 

 while even on these they seem to be more due to some pecul- 

 iarity of the shell structun than proper .surface sculpturing, the 

 >hell showing a disposition to crack along those curved lines. 



