INVERTEBRATES: 283 



interior unknown.) Length, about 0.60 inch; height, 0.20 

 inch; convexity, 0.14 inch. 



This shell is apparently so very closely allied to L. subscitula, of Meek and 

 Hayden (Trans. Albany Inst., vol. 4 — March 2, 1858), from Kansas, that we 

 would scarcely have ventured to regard it as a new species, were it not for the 

 widely different geological positions occupied by the two shells. The Kansas 

 species, however, is a little more convex, while its dorsal slope behind the beaks 

 is rather more concave in outline. It would probably also present other differ- 

 ences if we had specimens showing the surface markings. As the pallial line 

 has not been seen in either of these species, it is only provisionally that they 

 have been referred to the genus Yoldia. 



Locality and position : Waterloo, Monroe county, Illinois ; upper part of St. 

 Louis group of the Lower Carboniferous series. 



Genus Nuculana, Link, 1807. 



(Rost. Samml., iii, p. 155.) 



Nuculana? curta, M. and W. 



PI. 20, fig. 6 a, 6 b. 

 Leda curta, Meek and Worthen, June, 1861. Proceed. Acad. Nat. Sci., Philad., p. 144. 



Shell small, ovate, rather gibbous in the central and umbo- 

 nal regions ; anterior side abruptly rounded, the most promi- 

 nent point being at the middle; base semiovate, more promi- 

 nent in the antero-ventral region than behind; posterior side 

 abruptly contracted, so as to become subangular at the extrem- 

 ity; beaks elevated, incurved and nearly central; dorsal out- 

 line declining rather rapidly from the beaks, the anterior slope 

 being convex, and the posterior slightly concave; posterior 

 umbonal slope prominently rounded, or subangular from the 

 beaks to the narrow anal extremity. Surface ornamented by 

 very regular, closely arranged, concentric strise, about ten of 

 which may be counted in 0.05 of an inch. (Hinge and inte- 

 rior unknown.) Length, 0.32 inch; height, 0.21 inch; con- 

 vexity, about 0.19 inch. 



