170 UROCOPTIS, S. G. IDIOSTEMMA. 



Cyl. geminata PFR V Malak. Bl., xvii, 1870, p. 92; Monogr. y 

 viii, p. 441. ARANGO, Fauna, p. 122. 



This species varies widely in sculpture. The whole sur- 

 face has fine, sharp, slightly waved striae. On the upper half 

 there are rather close stout hollow ribs, swollen at the sutures,, 

 and often more or less extensively lost by erosion. At and 

 below the middle these ribs become sparser, or they become 

 weaker midway between sutures, leaving a series of oblong 

 bosses above and below the sutures. The last one to three 

 whorls may be either almost ribless, or there may be irregularly 

 developed ribs, as in the specimen figured (fig. 42). The last 

 whorl is either rounded beneath, or flattened, or even with 

 a spiral concavity, which Pfeiffer refers to in his description. 



The axis is very wide in the median whorls. It is en- 

 circled by a double cord with a median sulcus, and sculptured 

 with oblique nodes, as shown in fig. 53, which represents the 

 5th, 6th and 7th whorls from the base. It diminishes rapidly 

 above, slowly below, and within the last whorl is simple, with 

 merely a slight swelling. The shell ordinarily measures, 

 length 15, diam. 3.8 mm., and has about 11 whorls. 



44. U. INTUSMALLEATA ( c Gundl. ' Pfr.) PL 45, figs. 44, 45, 



46, 47. 



Shell cylindric, the upper third or fourth tapering to a 

 rather wide truncation; thin; gray- white; dull, sculptured 

 with narrow ribs, about one-third as wide as their intervals, 

 swollen drop-like at the ends; each interval sculptured with 

 about 4 (3 to 6) sharp thread-like striae. Whorls rather flat, 

 the suture impressed; last whorl shortly free in front, some- 

 somewhat flattened basally, subangular at the periphery. 

 Aperture obliquely short-ovate, the peristome expanded and 

 narrowly reflexed. Internal pillar moderately stout in the 

 intermediate whorls, constricted above and below near the 

 partitions, sculptured with wide-spaced, sigmoid, oblique ribs 

 connecting low spiral ridges running above and below in 

 each whorl (pi. 45, fig. 47, fourth whorl from base). In the 

 last two whorls this sculpture is obsolete, and above the pillar 

 rapidly tapers, becoming smooth (pi. 45, fig. 46, the 7th, 

 8th and 9th whorls from the base) . 



