157 



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

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

 lip and free, thus making the whole mass particularly uninviting 

 to any creature disposed to essay the destruction of the structure 

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

 Xenophoridre, the Yermelids, are as well protected by soldering 

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

 very distant appear to have no dependence but on their shefl. 



Genus XEXOPIIORA, Fischer de Waldheim, 1807. 



Shell conical, trochi form, upper surface carrying shells, stones 

 and madrepores, irregularly arranged, so as sometimes to almost 

 completely disguise the surface; imperforate or narrowly rimate ; 

 lower face of peripheral cnrina striate and granular. 



Tropical Seas. 



PAors,Montfort, 1810, and P*ew(/o^orws,Meek,are synonyms. 



Section TUGURIUM, Fischer, 1880. 



Shell umbilicated, only agglutinating in the neighborhood of 

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

 smootl^ below ; operculum trigonal or trapezoidal. 



Section ONTJSTUS, H. and A. Adams, 18") 1. 



Shell conical, depressed, widely and profoundly umbilicated, 

 periphery spinose at intervals, suture, towards the apex only, 

 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 Haliphsebus, Fischer, 1880. 



Subgenus ENDOPTYGMA, 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. UMBILTCATVJM, Tuomey. Cretaceous of Alabama. 



