MICROCERAMUS. 151 



I have not seen this species, which, according to Pfeiffer, 

 stands next to M. pazi, but is at once distinguishable by the 

 projecting, thread-like keel. 



Subfamily MICROCERAMIN.E Pilsbry. 



Jaw as in Urocoptinse; radula with very numerous teeth 

 in nearly straight transverse rows, the central tooth in each 

 row narrow, side teeth with long, narrow mesocones and very 

 small ectocones. Shell turrite, with entire, costulate apex 

 and incomplete peristome, the axis solid, not tubular or per- 

 forated. 



Genus MICROCERAMUS Pilsbry & Vanatta, 1898. 



Microceramus P. & V., Proc. A. N. S. Phila., 1898, p. 281 

 (July 12, 1898), type M. floridanus. Colobus ALBERS, Die 

 Hel., 1850, p. 177, for kieneri, cylindrus Gray, unicarinatus, 

 gossei, turricula and folliculus Pfr. (preoc.). Macroceramus 

 BINNEY, Terr. Moll., v, p. 384, and of authors generally. 



The shell is shortly rimate or imperforate, cylindric- 

 turrite or conic, composed of l l / 2 to 13 whorls; the apex is 

 ahvays entire, the nepionic shell composed of two vertically 

 ribbed whorls (pi. 15, fig. 6, M. floridanus} ; succeeding 

 whorls are obliquely rib-striate, or the later ones smoothish; 

 last whorl angular or rounded, the basal keel weak or want- 

 ing. The suture is usually crenulate or bordered with 

 papillae. Coloration of biown or corneous spots and streaks 

 on a whitish ground. The axis is slender, solid and straight 

 (except in subgenus Spiroceramus) . (Microceramus, a little 

 earthen vessel.) 



Jaw delicate, high-arched and composed of many narrow, 

 slightly imbricating plates, as in Urocoptis and allied genera 

 (pi. 14, fig. 4, M. pontificus). 



Radula rather long, proportioned about as in Urocoptis. 

 Teeth closely crowded, in nearly straight transverse rows. 

 The central tooth in each row has a very narrow basal-plate 

 and wider cusp, which is somewhat trefoil-shaped, and either 

 with almost no overhanging cutting point (M. pontificus, pi. 



