NO. 24 PTARMIGAN I A STRATA RESSER 23 



It will be observed that the several valves illustrated here and in 

 previous publications are within the normal variation of a species, 

 consequently this form is identified with the Spence shale species. 

 It has also been identified from localities near Brigham. 



Localities 54s, 5o,f, and 55c 



Plcsioty pes.— U.S.N. M. Nos. 51817, 51844. 



BILLINGSELLIDAE Schuchert 



WIMANELLA Walcott, 1908 



WIMANELLA MALADENSIS, n. sp. 



Plate 1, figs. 33-37 



Billingsella coloradoensis Walcott (part), U. S. Geol. Surv. Mon. 51, p. 751, 

 pi. 85, fig. 12, 191 2. 



Walcott figured the interior of an incomplete dorsal valve. Very 

 good specimens are available showing that the species is a typical 

 Wimanella, characterized by rather irregular but pronounced ribs. 

 The beak extends considerably beyond the hinge line, and the species 

 averages rather large. 



Localities 54s and 20.x. 



Cotypes.— U.S.N.M. No. 34776. 



GASTROPODA 



PALAEACMAEIDAE Grabau and Shimer 



HELCIONELLA Grabau and Shimer, 1909 



HELCIONELLA ARGUTA, n. sp. 



Plate 1, figs. 38-41 



This species is rather abundant. As may be seen from the illus- 

 trations, the shell is coiled into practically a complete whirl and 

 expands rapidly. The cross section for most of the whirl is nearly 

 circular but becomes flattened toward the mouth. The shell on the 

 inner side of the whirl is nearly smooth but on the opposite side is 

 divided by deep furrows into eight or more annulations, thus giving 

 it a much more rugose appearance than most species in the genus. 

 Each of these large rugosities carries a number of small transverse 

 plications. In addition the shell is strongly striated lengthwise, the 

 striae being slightly irregular in course, and varying slightly in 

 strength. 



Locality 54s. 



Cotypes.— U.S.N.M. Nos. o8486a-d. 



