MICROCERAMUS. 155 



2. M. CONCISUS (Morelet). PL 25, figs. 7-12. 



Shell very shortly rimate, cylindric-turrite or cylindric- 

 conic, the upper part corneous-brown with oblique, whitish, 

 thread-like stria?, the lower portion whitish with irregularly 

 scattered spots and dots and lunate streaks of corneous; the 

 last whorl or two usually somewhat smooth. Suture more or 

 less distinctly and coarsely papillose, each papilla at the 

 termination of alternate stria?, or sometimes formed by the 

 union of two. Whorls 9 l /2 to 12, convex, the last with a 

 barely indicated basal keel or none. Aperture rounded, the 

 peristome narrowly expanded. 



Length 11, diam. 4 mm., whorls 12 (Morelet, type). 

 Length 11.2, diam. 3.3 mm., whorls 12 (Tunkas). 

 Length 7.6, diam. 3.1 mm., whorls 9 1 / 2 (Tunkas). 

 Length 10, diam. 3 mm., whorls lli/o (Merida). 

 Length 6.7, diam. 2.7 mm., whorls 914 (Merida). 

 Yucatan (Morelet) ; at Izamal, Merida, Tekanto, Tunkas, 

 Ticul, Uxmal and Santa Ana, near Calcehtok (Heilprin ex- 

 ped.). Guatemala: Peten, on rocky hills (Morelet) ; Coban 

 (Sarg, Salvin). 



Cylindrella concisa MORELET, Testacea Novissima, i, p. 12 

 (1849). Macroceramus concisus Morel., PETIT, J. de C., i, 

 p. 379. CROSSE & FISCHER, Miss. Scient. Mex. Moll., i, p. 421, 

 pi. 18, f. 1, la, 16. PFR., Monogr., viii, p. 420. STREBEL, 

 Beitrag Mex., etc., iv, p. 90, pi. 5, f. 4c. (Coban) . PILSBRY, 

 Proc. Acad. Nat. Sci. Phila., 1891, p. 316. MARTENS, Biolo- 

 gia, Moll., p. 287. Macroceramus polystreptus TRISTRAM, 

 P. Z. S., 1861, p. 233, pi. 26, f. 11. PFR., Monogr., vi, p. 345. 

 This species, while closely related to the Antillean M. 

 gossei, differs in the narrower whorls, there being more in a 

 shell of the same length ; the sculpture is usually less coarse, 

 and the form of the well-grown specimens is more cylindric, 

 though small adults of both species are conic. That the de- 

 velopment of sutural papillns is extremely variable is shown 

 by the series of some hundreds of shells before me; and the 

 size varies within the wide limits familiar to all who have 

 studied large series of Urocoptida. Figures 8, 9, 10 are from 

 Tunkas specimens; fig. 11 from Santa Ana; fig. 12 a small 



