116 MACROCERAMUS, PORTO RICO, ETC. 



by a white border. Surface shining, sculptured with curved 

 riblets, narrower than their intervals. Whorls 12 to 13, 

 slightly convex, the last having a distinct cord-like carina at 

 the base. Aperture small, vertical, rounded-truncate; peris- 

 tome thin, slightly expanded, the columellar margin broadly 

 dilated, concave above. Columella conspicuously truncate be- 

 loiv. Axis strongly sinuous within. 



Length 15, total diam. 4, of last whorl above apert. 3.5 mm. 



Length 12.7, diam. 4, of last whorl above apert. 3.5 mm. 



St. Thomas: summit of the hill opposite Baker's, under 

 stones and on rocks (Bland, type locality) ; St. John (Bid.) ; 

 Tortola (Swift) ; Anageda (Swift) ; Porto Rico at San Juan 

 (Blauner). 



Cylindrella ? sp. undet., BLAND, in Adams' Contrib. to 



Conch., no. 11, p. 218 (Oct., 1852). Bulimus microdon PFR., 

 Monogr., iii, p. 365 (1853) ; P. Z. S. for 1851, p. 261 (Dec. 7, 

 1853); Conchyl. Cab., p. 127, pi. 42, f. 7-9. Macroceramus 

 m., SHUTTLEWORTH, Diagn., no. 6, Bern. Mittheil., 1854, p. 

 145. BLAND, Ann. Lye. Nat. Hist, of N. Y., vi, p. 71. PFR., 

 Monogr., iv, 689 ; vi, 350. CROSSE, J. de Conch., 1892, p. 25. 

 BALL & SIMPSON, Moll. Porto Rico, p. 377. 



The slender shape, attenuate above, the strong sculpture 

 and keel, and the truncate base of the columella, well distin- 

 guish this species. It should be compared with M. unicari- 

 natus (Lam.), but Delessert's figure of that species does not 

 show the characteristic columellar structure of microdon. 



The shells above described and measured are from St. 

 Thomas, the type locality, though Pfeiffer, in his original 

 paper, thought it was from Jamaica, probably because the 

 specimens were sent to him through C. B. Adams. This error 

 he subsequently corrected. Those from Tortola, St. John and 

 Anageda (fig. 71) are similar, but in the latter island a little 

 larger, 17 mm. long. 



In Porto Rico (figs. 72, 73) they vary from 13 to 19.5 mm, 

 long. The smaller examples are a little less strongly costulate 

 than typical microdon. The large shells may be separated as: 



