1917] The Ottawa Naturalist. 101 



Leptaena unicostata (Meek and Worthem), Figs. 7 A, a, B, b. 

 Types used for figures 11a, and lib, on plate IV, accompanying the 

 original description in volume III, of the Geology of Illinois, 1868. 

 From Maquoketa strata at Savannah, Illinois. Types numbered 

 12017 in the Worthen collection at the University of Illinois, and 

 examined owing to the courtesy of Prof. T. E. Savage. Figures in- 

 troduced here for comparison with Raftnesqaina breviusculus. Notice 

 the relative flattening of the greater part of the pedicel valve, the 

 geniculation of the anterior part of both valves, the straightening of 

 the anterior margin and the consequent angulation of the anterior 

 outline on both sides of this straightened part. The radiating stria- 

 .tions, although numbering 4 or 5 in a width of one millimeter, are 

 distinctly leptaenoid, being broad and flat and separated by very 

 narrow interspaces. 



Raeinesquina breviusculus, sp. now, Figs. 6 A, B, b, C, c, D. 

 The size and general outline of this species is sufficiently indicated by 

 the accompanying illustrations. Figures b and c indicate the amount 

 of curvature, along the median line, of the exterior of the pedicel and 

 brachial valves illustrated by figures 6 B and C. The interior of the 

 brachial valve is thickened along the anterior margin along a narrow 

 area crossed by vascular markings, and here the interior of the shell 

 has a somewhat leptaenoid appearance. However, there is no genicula- 

 tion such as that characteristic of the genus Leptaena. The curvature 

 of the pedicel valve increases slightly toward the beak and much more 

 rapidly toward the anterior border. The muscular area of the pedicel 

 valve, not figured, is broad and flabellate, similar to that of other 

 species of Rafinesqitina, but only weakly defined. From 4 to 6 radi- 

 ating striae occur in a width of one millimeter at a distance of 20 

 millimeters from the beak, averaging about 5 in one millimeter. The 

 median striation often is more distinct than the remainder, but not 

 prominent. Common in the upper part of the argillaceous Richmond. 

 Readily distinguished from Strophomena parvula, in the same strata, 

 by the convexity of the posterior parts of the pedicel valve. 



Raitnesquina pergibbosa, nov. sp., Figs. 8 A, B, C, D. Pedicel 

 valve strongly convex, almost hemispherical in the more* obese speci- 

 mens, with the greatest convexity about two-fifths of the length of the 

 shell from the beak. This strong convexity is maintained to within 

 a short distance of the postero-lateral angles and sometimes produces 

 an abruptly auriculate appearance here. The more prominent radiat- 

 ing striations occur at intervals of less than a millimeter, and the 

 intermediate spaces are occupied by three much finer striae. The 

 interior markings of the brachial valve are boldly defined and are 

 well represented by the accompanying figures. Usually there is a 

 well defined ridge parallel to the anterior prolongation of the median 



