206 CERION, GROUP V. 



lete), below which radial wrinkles replace the ribs. Aperture 

 rounded-ovate, flesh-colored inside, the peristome reflexed. Parietal 

 lamella short, small or subobsolete ; axial lamella hardly or not visi- 

 ble in front, weak within the last whorl. 



Length 30, diam. 16 mill, (type of dimidiata Pfr.). 



Length 25^, diam. 18 mill. 



Length 27, diam. 16 mill. 



N. coast of prov. Santiago de Cuba, at Gibara (Gundlach). 



Pupa dimidiata PFR., Zeitsch. f. Malak., 1847, p. 16; Monogr., 

 ii, p. 316 Pupaproteus Gundl., PFR., Malak. Bl., vii, i860, p. 19 ; 

 Novit. Conch., p. 267, pi. 66, f. 13-22; Monogr., v, p. 291 AR- 

 ANGO, Fauna Malac. Cubana, p. 101. SOWERBY, Conch. Icon., xx, 

 pi. i f f. 4. Strophia (Pinguitia} dimidiatia Pfr., MAYNARD, Con- 

 trib. to Sci., iii, p. 30, pi. 6, f. 6, 7 (March, 1896). 



The name dimidiatum was originally applied to a rather long and 

 cylindric form, while proteus was based upon the shorter and more 

 strongly characterized shells. Pfeiffer abandoned the former name 

 because he considered it to apply to a non-typical form of the species. 

 The original description follows : 



'* Shell rimate, cylindric-ovate, solid, having distant and arcuate 

 folds, dull white. Spire bee-hive shaped, the apex shortly conic ; 

 suture shallow. Whorls 11, narrow, rather flat, the upper smooth, 

 the last bipartite, subcarinate in the middle, marked below the angle 

 with several impressed, crowded, spiral lines, and densely striated 

 from the center, the base swollen. Aperture nearly semicircular, 

 peristome thickened, expanded, the margins joined by a straight 

 callus, right margin subauriculate. Length 30, diam. 16 mill.; ob- 

 lique length of aperture with peristome 13, width 11 mill." (Ptr.). 



The shortest specimen I have seen measures 22x16 mill., and has 

 9^ whorls (fig. 31); the largest is 32x17 mill., with 1 1 whorls. Aside 

 from this great variation in size and proportions, there is variation 

 in sculpture, some shells before me totally wanting ribs (fig. 32). 

 The keel defining the base is also variable, and sometimes entirely 

 wanting. All forms of the species are distinguished by the very low, 

 wide cone of the spire. 



There is a much less differentiated form of the species, in which 

 the cylindric shell is regularly sculptured with nearly straight ribs, 

 which may be quite numerous with intervals of their own width (pi. 

 28, fig. 33) or rather spaced (pi. 28, fig. 34); the number of ribs 



