THE CYCLOPHORID LA^STD MOLLUSK.S OF AAIEIRICA 49 



Type: Megalomastoma hrunnae (Guilding) S^2i\nso\\=Megalo- 

 mastoma {Megalomastoina) hrunneum (Guilding) Swainson. 



KEY TO THE SPECIES OF SUBGENUS MEGALOMASTOMA 



Shell elongate-conic. 



Axial ribs of early whorls closely spaced antillarum 



Axial ribs of early whorls not closely spaced brunneum 



Shell elongate-ovate petiti 



MEGALOMASTOMA (MEGALOMASTOMA) ANTILLARUM (Sowerby) 



Plate 9, Figukes 10-12, 21 



1843. Cyclostoma antillarum Soweebt, Thesaurus conchyliorum, vol. 1, p. 150, pi. 

 28, fig. 180. 



Shell small, elongate-conic, chestnut-brown with the peristome 

 white. The nucleus consists of a single smooth turn. The early 

 postnuclear whorls are inflated and strongly rounded ; the later ones 

 a little less so, marked by moderately elevated, slender, sublamellar, 

 retractively slanting axial ribs, which are very regular on the first 

 two turns and rather closely spaced ; on the later turns they are much 

 more distantly spaced and there is a tendency for finer threads to 

 appear in the broad interspaces. Suture strongly constricted. Per- 

 iphery well rounded. Base protracted, openly umbilicated, and 

 marked by a moderately strong, broad, rounded cord at the outer 

 limit of the umbilicus, which is crossed by the axial ribs. Aperture 

 subcircular; peristome not on a flat plane, but sinuous, moderately 

 thickened and reflected, and moderatel}^ excised on the parietal wall. 

 Operculum typically megalomastomid. 



The specimen described and figured is one of a lot, U.S.N.M. No. 

 393653. It was collected by me on Mount Sage, Tortola, British 

 West Indies. It has 7.5 whorls and measures: Height, 13.6 mm.; 

 greater diameter, 5.1 mm. 



This species recalls closely M. (M.) hrunneum (Guilding) Swain- 

 son, from which it can be distinguished readily by its smaller size 

 and more closely spaced axial ribs on the early turns. The umbilical 

 cord is also less pronounced. 



MEGALOMASTOMA (MEGALOMASTOMA) BRUNNEUM (Guilding) Swainson 

 Plate 9, Figxikes 7-9, 22 



1840. Megalomastoma hrunnea (Guilding MS.) Swainson, A treatise on ma- 

 lacology, pp. 186, 336, fig. 97, g, h, i. 



Shell elongate-conic, chestnut-brown, with the peristome white. 

 Nuclear whorls 1.2, well rounded, smooth. The early postnuclear 

 whorls inflated ; the later ones less so and the last one flattened, marked 

 by very decidedly retractively curved, slender, sublamellar axial ribs, 



