216 ONUSTIDiE. 



admirably adapted to to the nature of the floor on which they 

 live,, which is usually composed of the debris of dead shells. 



Onustus, H. and A. Adams, 



Syn. — Haliphoebus and Tugurium, Fischer. 



Dist7\ — Several sp. Tropical ; East and West Indies. 0. 

 solayHs, Linn. (Ixvi, 31, 32). Fossil. Devonian — . 



Shell conical, trochiform, depressed, widely and profoundly 

 umbilicated ; periphery of the whorls fringed with regularly 

 disposed tubular spines or slight projections ; pieces of small 

 shells agglutinated upon tlie whorls at the sutures, where they 

 are attached as growth continues. 



B^TROCHUS, Whitfield, 1882. 



Distr. — E. concava^ Hall. Carb. ; Ind., Ills. 



Shell conical above, flat or concave beneatli, and broadlj^ and 

 deeply umbilicated ; aperture very oblique, and the outer angle 

 of volutions strongly carinated or expanded ; surface ornamen- 

 tation unlike on the upper and lower surfaces. 



Differs from the umbilicated forms of Trochidse in not forming 

 a columella ; the lower or basal surface sloping gradually and 

 smoothly into, and forming the sides of, the umbilicus, giving an 

 obliquely elliptical section to the volution. 



Xenophora, Fischer de Wald. 



Sijn. — Phorus, Montf Pseudophorus, Meek. 



Distr. — Several sj). Tropical. X. conchyliophora, Born 

 (Ixvi, 33). Fossil. Devonian — . 



Shell conical, trochiform, whorls flattened, carrying shells, 

 madrepores and stones, miscellaneously arranged and attached 

 anywhere upon the exterior surface, so as to completel}^ disguise 

 the dorsal aspect of the shell ; lower surface free of extraneous 

 agglutinations ; umbilicus narrow, sometimes covered by the 

 inner lip. 



The " carriers " inhabit deep water, and are most numerous in 

 the Java and China Seas. Each species appears to have its own 

 peculiar method of collecting the fragments of shells and stones 

 which cover the ground where it lives, and each cements to the 

 outside of the shell its particular kind of materials. The adven- 

 titious pieces of shell are so disposed as not to curve downwards 

 beyond the edge of the shell, so as to impede the progress of the 

 animal, but are usually placed with their concave sides upper- 

 most, and the purpose of this structure is evidently concealment 

 of the true nature of the animal, either for attack or defense, or 

 perhaps for both occasions ; as when tricked out with shells and 

 stones it may well be mistaken for a refuse-heap. 



ENDOPTYGMA, Gabb, 181T. Differs from Xenophora in having 



