MACROCERAMUS, PORTO RICO, ETC. 115 



Urocoptis or Brachypodella are comparatively enormous. The 

 jaw is entirely similar in all the genera of Urocoptince. 



The shell is like that of Microceramus in shape and orna- 

 mentation, but differs in the smooth nuclear whorls, so that 

 when any of these are retained, as is usually the case, Macro- 

 ceramics can at once be distinguished from Microceramus by 

 this feature of the initial whorls, aside from the diverse 

 radula. 



Cochlicellus siibantiquatus Beck, Index Moll., p. 63, no. 10, 

 is a nude name, probably based upon some species of Macro- 

 ceramus. 



In Haiti the genus is represented by three groups of species : 

 the groups of M. tenuiplicatus, of M. klatteanus, and of M. 

 lineatus. The first of these has no Cuban representative ; the 

 second is represented in Cuba by the pupoides group, and in 

 part by the pazi group, but the latter also approaches the 

 Haitian group of M. lineatus. Cuba also has another group, 

 that of M. canimarensis, unrepresented in Haiti ; and a some- 

 what similar group also occurs in Porto Rico and eastward, 

 that of M . microdon, which however stands near the Haitian 

 group of M. klatteanus. Eastern Cuba and Haiti, in short, 

 support a nearly homogeneous fauna of Macroceramus species, 

 about equally differentiated in the two areas. East and west 

 from this centre the species diminish very rapidly in numbers 

 and variety. 



The general sequence of groups given below is from the 

 east westward. 



1. Species of Porto Rico and islands eastward, no. 1 to 3. 



2. Species of Haiti, no. 3a to 17. 



3. Species of Cuba, no. 18 to 35. 



SPECIES OF PORTO Rico AND ISLETS EASTWARD. 



Group of M. microdon. 

 1. M. MICRODON (Pfeiffer). PI. 24, figs. 71-74. 



Shell very shortly rimate, slender, turrited, thin, the out- 

 lines of the spire slightly convex. Brown-tinted whitish, with 

 irregularly-spaced longitudinal brown streaks, each preceded 



