Xll UROCOPTID^E. 



less cylindric, and composed of many narrow whorls. In 

 only very few species, such as Pineria viequensis (xvi, pi. 1), 

 it is markedly conic, and the number of whorls is reduced. 

 It is dextral as a general rule, but a few species are sinistral 

 (Urocoptis scceva, xv, 195; U. coronadoi, xv, 218; Brachy- 

 podella agnesiana, xvi, 98; B. diminuta, xvi, 100; B. chem- 

 nitziana, xvi, 106; B. gracilis, xvi, 107). 



In many genera the early whorls are abandoned by the 

 soft parts in the adult stage. The mantle and liver tissue 

 occupying these whorls are not renewed with new. cells, and 

 hence an empty space is left. This is partitioned off from 

 the living portion by a flat or convex septum. Being de- 

 prived of organic connection with the mantle, it becomes dry 

 and brittle, and in course of time is usually broken off. 

 Occasional individuals of species normally truncate by chance 

 retain the spire complete; but in all such shells the par- 

 tition or septum may be found at the appropriate place. In 

 some cases there may be several septa and successive trun- 

 cations ; but so far as my observations go, there is, as a rule, 

 in Urocoptida only one partition formed. The spire may 

 break off down to the partition, as in the Jamaican group 

 of Urocoptis, or an empty whorl or two may persist above 

 it, as in the Haitian Autocoptis. The number of whorls 

 amputated may exceed the number retained, or (as in Macro- 

 ceramus) only the very apex is broken. In this case the 

 utility of the operation is lost, and it lingers on in some of 

 the species merely as the reminiscence of an obsolete func- 

 tion. There is no evidence that shell-substance is absorbed 

 at the point of breakage. The immature shell is invariably 

 thin, and the fragility incident to the loss of organic con- 

 nection with the mantle fully accounts for its fracture. Some 

 genera, such as Holospira, Pineria, Microceramus, are never 

 truncate; their early whorls are less slender, the cone of the 

 spire shorter, than in truncate genera. The prevalence of 

 spire-amputation in many non-related groups of the family 

 probably indicates a polygyrous, truncate, ancestral stock 

 for the whole. The number of whorls, in either entire or 

 truncate shells, is subject to a wide range of individual 

 variation. 



