34 TJniversity of Michigan 



Radula (fig. ix-25) : B; A/2-3, B/2-3, C/3, D/3, E; 

 M 5-6/1, 2-3/2, 1/3, (13-15/3 +) =23-25; total 57-61. 

 Rhachidian central : broadly shield-shaped with raised, an- 

 terior margin. A-central: somewhat similar to that of 

 Stoastoma,^^ bnt with two, stont, aculeate cusps and some- 

 times a minute accessory one. B-central : similar to A-central 

 but with more ovoid base. C-central: elliptical with 

 two, stout, aculeate cusps on the reflected, anterior end, and 

 usually a small, outer one. D-lateral : similar to Stoastoma 

 but with only two very heavy cusps and a third, vestigial one 

 either outside or inside of these. E-lateral: similar to 

 Stoastoma but stouter and heavier. Marginals: 23 to 25, of 

 which the 5 or 6 inner are unicuspid, 2 or 3 are bicuspid, 1 is 

 tricuspid, and the others of the series increase the number of 

 cusps rapidly; the outermost uncini are broad and multi- 

 cuspid plates as is characteristic in the Helicinidae. 



What I take to be the males are smaller and more de- 

 pressed than the dimensions given below. 



Dimensions'^ 



Shell Aperture Calcareous Operculum 



altitude major diam. altitude diameter length width 



2.14 109 (2.34) 42 (.91) 143 (1.31) 44 (.94) 79 (.74) 



This monotypic genus combines, to a remarkable degree, 

 the shell and operculum of Eutrochatella, subgenus Pyrgo- 

 domus, with the radula of Stoastoma. In general appearance, 

 the shell most closely resembles the Cuban species, E. continua 



32 1922; Proc. Acad. Nat. Sci. Philadelphia, LXXIV, p. 58, fig. vi-26. 



33 Throughout this paper, the altitude of the shell is given in milli- 

 meters, but the other dimensions are expressed as indices, followed by the 

 actual measurement (in parentheses). The index of the major or minor 

 shell diameters, the altitude of the aperture, or the length of the operculum, 

 is the percentage obtained on division by the altitude of the shell. The 

 index for the diameter of the aperture is similarly taken in terms of its 

 altitude, while that of the operculum is in terms of its length. Unless 

 otherwise stated, all dimensions are outside measurements. Altitudes are 

 scaled parallel to the central axis of the shell, while the major and minor 

 diameters are at right angles to this and to each other. Lengths are 

 major dimensions, and widths are measured at right angles to them. 



