THE CYCI^OPHORID LAJSTD MOLLUSOELS OF AIvIElRIOA 51 



the parietal wall and in having the early postnuclear sculpture as in 

 typical Megalomastoma^ while that of the later turns has the axial 

 ribs broken up into elongated, somewhat lunate tubercles, which gives 

 to the surface of these whorls a rasplike appearance. Operculum a 

 simple, thin, multispiral chondroid plate. 



Type : Gyclostoma {Megalomastoma) verruculosuin Shuttleworth= 

 Megalommtoma {MegaloTiuDstomoides) ver7mculosvm (Shuttleworth). 



Distribution: Puerto Rico. 



MEGALOMASTOMA (MEGALOMASTOMOIDES) VERRUCULOSUM (Shuttleworth) 



PiATE 9, Figures 13-15, 19 



1854. Gyclostoma {Megalomastoma) verruculosum Shuttleworth, Berner Mitth., 



p. 90. 

 1864. Megalomastoma verruculosum Sowekby, Thesaurus conchyliorum, vol. 3, pi. 

 263, fig. 15. 



Shell small, elongate-conic. Nuclear whorls decollated in all our 

 specimens. Postnuclear whorls well rounded, the early ones marked 

 by slender, retractively curved axial riblets, which are about as wide 

 as the spaces that separate them. On the last three turns these riblets 

 break up into segments and give to the surface a rasplike appearance. 

 Suture strongly constricted. Periphery well rounded. Base pro- 

 duced, openly flatly umbilicated, and marked by a strong spiral cord 

 at the outer limit of the umbilicus, which is crossed by the axial rib- 

 lets, which extend over the umbilical wall. Aperture circular, not in 

 a single plane, but sinuous; peristome thickened and somewhat re- 

 flected, of equal width all around, not incised on the parietal wall. 

 Operculum multispiral, corneous, with central nucleus. 



We have this species from Puerto Rico without specific locality. 



The specimen described and figured, U.S.N.M. Xo. 535944, has 7 

 whorls remaining and measures : Height, 15.1 mm. ; greater diameter, 

 5.7 mm. 



This shell is small like typical Megalomastoma but differs from it 

 markedly by the sculpture and the absence of excision on the parietal 

 wall. 



Subfamily Diplommatininae Kobelt 



This subfamily is defined in the key on p. 43. 



Genus ADELOPOMA Doering 



For definition of the genus, see p. 148. 



