52 COELOCENTRUM, SUBG. SPARTO CENTRUM. 



specimens known. Regularly ribbed, the ribs about as wide 

 as the intervals, a little arcuate, and about 4 in the length of a 

 mm. on the penultimate whorl. Number of whorls unknown, 

 as those with fully-formed apertures are decollate, with no 

 closing septum above, and therefore it is impossible to state 

 whether the shell is normally subject to autotomy or has an 

 entire spire. In the type specimen (fig. 15) there are nearly 

 12 whorls; in another, more perfect individual (pi. 17, fig. 24) 

 there are 13, and judging by allied species, about six have been 

 broken off. "Whorls convex, the last having the Base a little 

 flattened and smoother, or strongly convex with undiminished 

 ribbing, a cord running around the verge of the umbilical area, 

 but with no subperipheral cord. Aperture subvertical, 

 rounded below, straightly truncate above. Peristome well 

 expanded, the columellar margin broadly dilated, parietal 

 margin adnate to the preceding whorl. 



The internal pillar is smooth, somewhat sigmoid within each 

 whorl, there being a strong median spiral bulging or swelling. 

 The hole above has a diameter of about 0.8 mm. in a specimen 

 broken to 3% whorls (fig. 16). 



Length (broken) 19, diam. 4.2 mm. (type). 



Length (broken) 21.6, diam. 4.8, longest axis of apert. 4, 

 width 4 mm. 



Muleje, on the east coast of Lower California, below 27 de- 

 grees latitude, under loose volcanic rocks (W. M. Gabb). 



Cylindrella (Urocoptis) irregularis GABB, Amer. Journ. of 

 Conch, iii, p. 238 (in part), pi. 16, f. 4 (Jan. 2, 1868). C. 

 (Gongylostoma) irregularis BINNEY, Land and Fresh-water 

 Shells of N. A., i, p. 23, fig. 17. PER., Monogr., viii, p. 448. 

 Holospira irregularis TRYON, Amer. Journ. Conch, iii, p. 313, 

 pi. 21 (15), fig. 30; Monogr. Terrestr. Moll. U. S., p. 140, pi. 

 15, f. 30. Ccelocentrum irregulare FISCHER & CROSSE, Moll. 

 Mex., i, p. 349, pi. 17, f. 10 (fragment). PILSBRY, Proc. 

 A. N. S, Phila., 1900, pp. 553, 554, f . 3, 4. 



Differs from other Lower Californian species in having the 

 last whorl adnate to the preceding to the aperture, with no 

 tendency to become free. The aperture is but slightly oblique, 

 and differs from the other species in shape. There are 58 



