CERION, GROUP XIII. 275 



f. 3, 4 KtfSTER, Conchyl. Cab., p. 80, pi. 11, f. 18 (=ianthina 



Mayn.). SOWB., C. Icon., pi. 3, f. 23 a, b. Strophia cylindrical 

 MAYNARD, Contrib. to Science, iii, p. 34, pi. 7, f. 2, 4 (March, 1896>. 

 Strophia ianthina MAYN., Contrib. to Sci. i, p. 69, pi. 2, f. 1.3 (July, 

 1889). S. pattida MAYN., t, c., p. 70, pi. 2, f. 14. 



The typical form is rather fine-ribbed, but the variation among 

 specimens from one place is astonishing, though there are doubtless 

 fine- and coarse-ribbed colonies. The teeth or lamella? are also 

 exceedingly variable among fully adult and externally similar shells. 

 The outer or spiral lamella, while typically long, is often reduced to 

 a length of one or two mill., and sometimes the inner or infra-parietal 

 lamella is short or even wholly obsolete. Maynard's S. cylindrica is 

 a synonym of typical C. rubicundum. 



Form ianthinum Mayn. (pi. 45, figs. 91, 92, 93). Usually dull, 

 dark purple between white ribs, becoming orange or rose above ; 

 ribs wide-spaced, about 24 on the penult, whorl ; the shell often more 

 slender than rubicundum. Type locality, " rocky plains between the 

 elevations that skirt the southern shore of Inagua, and the extensive 

 salt lake of the interior, about 20 miles from Matthewstown, on the 

 scattering shrubbery." 



Form pallidum Mayn. (pi. 45, fig. 94). Externally flesh-color, 

 deepening to pale purple on the lower whorls, the peristome, riblets 

 and apex white ; interior pale purple. Riblets rather wide-spaced, 

 23 on the penult, whorl. Type locality, " the cultivated fields that 

 lie on the slopes of the hills that border the southern shores, between 

 15 and 20 miles from Matthewstown," Inagua. 



Both of these forms have the Iamella3 as in C. rubicundum. 



Var. IIETERODON Pilsbry, n. v. PI. 45, figs. 96, 97, 98. 



Shell small and thin, roseate with white ribs, or maculate with rose 

 over part of the ribs. Sculpture of densely crowded, fine riblets, 46 

 to 48 on the penult, whorl. Whorls 8^. Lamellae as in C. stria- 

 tellum a short parietal not connected with a somewhat longer spiral 

 lamella, with a small, short infra-parietal adjacent to the neighboring 

 ends of the other lamellae. Length 14 to 15, diam. 6 mill. 



Inagua (R. Swift). 



This is as " good" a species as any of the Diacerions, but while I 

 have not seen intermediate specimens, I believe it to be a dwarf form 

 of the rubicundum stock. The four specimens are essentially alike. 



