XENOniORID^E. 157 



surface for their weight than univalves, and as the back affords 

 the best surface for attachment, the interior of these is turned 

 up and free, thus making the whole mass particularl3'^ uninviting 

 to any creature disposed to essay the destruction of the structure 

 with a view to molluscous food. Tlie near relatives of the 

 Xenophoridae, the Yermelids, are as well protected by soldering 

 their shells to the surface of large bodies, but other groups not 

 ver}- distant appear to have no dependence but on their shell. 



Genus XENOPIIORA, Fischer de Waldhcim, 180T. 



Shell conical, trochiform, upper surface carrying shells, stones 

 and madiepores, irregularl}' arranged, so as sometimes to almost 

 completely disguise the surface; imperforate or ndrrowly rimate ; 

 lower face of peripheral carina striate and granular. 



Tropical Seas. 



PAo7-i/s,Montfort, 1810, and r,<ei(do2iJio7'us,'Mee\i^iire synonj^ms. 



Section Tugurium, Fischer, 1880. 



Shell umbilicated, onl^^ agglutinating in the neighborhood of 

 the suture, margin of the last whorl prolonged, thin, blade-like, 

 smooth below; operculum trigonal or trapezoidal. 



Section Onustus, H. and A. Adams, 1854. 



Shell conical, depressed, widely and profoundl}- umbilicated, 

 periphery splnose at intervals, suture, towards the apex onl}-, 

 more or less ornamented with small stones or shells agglutinated 

 to the surface. Tropical Seas. 



Humphrey first used the faulty generic name (being an adjec- 

 tive), in 1797, but the justifiable exclusion of this author's genera 

 does not prevent its use in connection with the recognizable 

 definition of H. and A. Adams ; hence I see no absolute neces- 

 sity for adopting instead Halipha?bus, Fischer, 1880. 



Subgenus En'DOPTygma, Gabb, 1877. 



Shell umbilicated, agglutinating, the basal margin having one 

 or two internal spiral plications, which have left their imprint on 

 the cast from which the group is described. 



E. UMBiLiCATUM, Tuomcy. Cretaceous of Alabama. 



