48 BULLETESr 181, UNITED STATES NATIONAL MUSEUM 



white. Nuclear •whorls 2, small, well rounded, smooth. The first 

 2 postnuclear whorls rather strongly inflated, the rest gradually less 

 inflated and finally flattened. The postnuclear whorls are marked 

 by closely spaced, decidedly retractively curved, slender axial riblets, 

 which are about as wide as the spaces that separate them. Suture 

 rendered conspicuous by the feeble shoulder of the whorls. Periph- 

 ery well rounded. Base decidedly protracted, openly umbilicated, 

 marked by a somewhat obsolete cord at the outer limit of the umbili- 

 cus. The umbilical wall marked by the continuation of the axial 

 riblets. Aperture subcircular ; peristome thickened and reflected, nar- 

 rower on the columellar wall than on the rest. Operculum typically 

 farcimoid. 



The specimen figured is one of a large series, U.S.N.M. No. 151351, 

 from the Salle collection, probably a topotype. It has 8.4 whorls 

 and measures: Height, 28.2 mm.; greater diameter, 11.5 mm. The 

 locality mentioned is Haiti, the designation for all Hispaniola in the 

 early days. We know Salle collected only in the Santo Dominican 

 region, so the species must be referred to the Dominican Eepublic. 



All our other lots are equally deficient in specific locality data. 



Genus MEGALOMASTOMA (Guilding) Swainson 



1840. Megalomastoma (Guilding) Swainson, A treatise on malacology, pp. 186, 

 336, figs. 97 g, h, i. 



Shell small, cylindroconic, covered with a persistent periostracum. 

 Nuclear whorls smooth, the succeeding turns marked with strongly 

 elevated, retractively curved axial riblets. Base with a strong spiral 

 keel at the outer limit of the broad open umbilicus. Aperture sub- 

 circular; peristome double, with a rather deep, somewhat lunate ex- 

 cision on the parietal wall. Operculum a simple, thin, multispiral, 

 chondroid plate. 



Type: Megalornastoma hninnea (Guilding) Swainson=iI/ep'«?<?- 

 mwitoma {Megalomastoma) hrunnemn (Guilding) Swainson. 



This genus ranges from St. Thomas through St. John to Tortola. 



The radula of Megalomastoma {Megalomastoma) petiti has the 

 formula 3:3:3:3. The jaw has a median projection, and the verge 

 is attached to the side of the neck, gradually tapering without a 

 terminal appendage. It is traversed by a seminal groove. 



KEY TO THE SUBGENERA OF MEGALOMASTOMA 



Last whorl axially ribbed Megalomastoma 



Last whorl axially tuberculated Megalomastomoides 



Subgenus Megalomastoma (Guilding) Swainson 



Megalomastomas having the surface with axial ribs only, and with 

 the peristome excised on the parietal wall. 



