372 PROCEEDINGS OF THE ACADEMY OF [PaRT II 



The infrasutural tubercles are seen on two to four whorls, but 

 they are very weak except in the last whorl, or sometimes the last 

 two. They may disappear for a half whorl, to reappear later. In 

 some examples there are only weak traces of tubercles, and these 

 appear to form a transition to C. gurabense Maury. In all there is a 

 minute but distinct spiral striation, either nearly even, or sometimes 

 about every eighth thread is slightly larger. 



Length as broken 27, diam. 13 mm. Type no. 4074, figs. 10-12. 



Length as broken 26, diam. 11.5 mm. Fig. 9. 



The loss of the last half whorl makes the diameter much less 

 than in a perfect shell. 



A peculiar specimen, no. 4075, in which the last whorl is rather 

 short and rounded, and the subsutural tubercles very small, is photo- 

 graphed in Plate XXXIII, figs. 18, 19. It is a young shell, perhaps 

 referable to C. o. ventricosior . 



Length 25, diam. 13 mm.; 8 whorls. 



Cerithium obesum harrisi n. var. Plate xxxiii, figs. 14, 15. 



A variety which may be called harrisi, was found among unas- 

 sorted shells. It seems to be a degenerate form, perhaps from an 

 unfavorable station. It is smaller, narrower, covered with slightly 

 unequal spiral striae; there are about 6 tubercles on the back of the 

 last whorl. The suture rises steeply towards the aperture. 



Length 22, greatest diam. 9.4, antero-postei'ior diam. 7.6 mm. ; 

 10| whorls. 



Type no. 4073 A. N. S. P. 



Cerithium (obesum?) giu-abense Maury. Plate xxxiii, figs. 13, 17. 



In another form the size is about the same as the last, but alter- 

 nate threads are granose. On the last whorl there are infrasutural 

 tubercles, on those preceding, two series of enlarged granules. This 

 appears to be C. gurabense Maury. 



Length as broken 20 mm.; diam. 7.5 mm. 



Cerithium simplex Gabb. Plate xxxiir, fig. 7. 



Cerithium simplex Gabb, Tr. Am. Philos. Soc, xv, 1873, p. 238. 

 ? Cerithium obesmn Gabb, Guppy, Q. J. Geol. Soc, xxxii, 1876, p. 519, pi. 29, 

 fig. 9. Not of Gabb. 



A species of simple, conic form, without varices on the later whorls, 



though some very low, inconspicuous ones may be seen on the upper. 



It is spirally grooved, the intervals slightly convex and very unequal, 



not in the least granose. 



