518 bulletin: museum of comparative zoology. 



the middle. The brachial shell, except in the umbonal region, follows 

 the curvature of its opposite. The striae of the umbonal region are 

 of uniform size, but towards the front they show distinct alternations, 

 and there are from one to three fine striations between each pair of 

 coarse ones, the number varying with the distance from the margin. 

 When the shell is partially exfoliated, rows, of conspicuous pores are 

 disclosed in the furrow^s between the striae. Some specimens show 

 distinct wrinkles on the sides near the hinge. Some are located 

 nearly at right angles wdth the hinge, others diagonally, the variable 

 position suggesting pathologic origin for these features. 



Mcosnrcmc7its: — A specimen from the Lower Maquoketa near 

 Clermont is 41 mm. long, and about 65 mm. wide; one figured by 

 Winchell and Schuchert is 40 mm. long and 60 mm. wide. 



Rafinesquina alternata var. loxorhytis w^as a name suggested by Meek 

 (Pal. Ohio, 1873, 1, p. 91) in a brief description which was not accom- 

 panied by a figure. The variety does not appear to have been identi- 

 fied successfully away from Cincinnati, and, as Cumings has remarked, 

 (32d Ann. rept. Dept. geol. nat. res. Indiana, 1908, p. 928) the charac- 

 teristic which appeared most important to the describer may not be a 

 reliable one. Meek relied upon the extended form and obliquely 

 wrinkled lateral extremities for the identification of this variety, but 

 oblique wrinkles near the cardinal margin have proven in many cases 

 to be the accompaniment of individual senescence or result of accident. 

 The specimens from the Richmond of Indiana identified as R. alternaia 

 loxorhytis by Cumings lacked the WTinkles. 



Winchell and Schuchert found a large Rafinesquina at Spring 

 Valley, Minnesota, which they illustrated under this name, but which 

 has recently been referred to R. kingi Whitfield (Bassler, Bull. 92, 

 pt. 2, U. S. N. M., 1915, p. 1087.) If Whitfield's description and 

 illustrations are correct, then the Minnesotan form cannot be R. 

 kingi, for its author stated that that species showed no alternations of 

 striae, and the figure show^s the Wisconsin shell to be much longer than 

 that from Minnesota. 



Comparison with R. alternata loxorhytis cannot be satisfactory in 

 our present ignorance of that variety, but Meek described it as having 

 acutely angular, flattened, scarcely deflected cardinal angles, while 

 the present species has convex "ears" which are set off by a conspicu- 

 ous depression. It also has a much broader form than any of the 

 shells which are usually designated as varieties of R. alterriata. 



Locality: — In the Maquoketa near Spring Valley, IVIinnesota, 

 and Clermont, Iowa; rare at the latter place. 



