HISPANIOLAN AND BAHAMAN ANNULARIIDAE 225 



the turns. Most of these riblets become expanded into a sharp cusp at 

 the summit. The spiral sculpture consists of not very strongly developed 

 threads, of which 7 are present on the first and 10 on the remaining 

 turns. Suture strongly constricted. Periphery inflated, strongly rounded. 

 Base short, inflated, strongly rounded, openly umbilicated, and marked 

 by the continuation of the axial ribs and five spiral threads. Within the 

 umbilicus eight additional spiral threads are present. Last whorl solute 

 for about one-third of a turn. Aperture subcircular; peristome double, 

 the outer broadly, flaringly expanded, a little wider on the inner lip 

 than the outer, with an auricle at the posterior angle of the aperture in 

 the middle of which the breathing siphon is situated ; inner peristome 

 exserted and slightly expanded. Operculum? 



The type (U.S.N.M. No. 355429) was collected by Bartsch on John 

 Flower Key, Middle Bight, Andros Island, Bahamas. It has a little 

 more than 3 whorls and measures : Length, 9.0 mm. ; greater diameter, 

 5.3 mm. ; lesser diameter, 4.0 mm. 



The solute last whorl and the very distantly spaced ribbing will dis- 

 tinguish this species from all the other Opisthosiphons. 



I take pleasure in naming this unique species for the late Dr. Alfred 

 S. Mayor, former director of the Marine Biological Laboratory at the 

 Tortugas, of the Carnegie Institution. 



OPISTHOSIPHON (OPISTHOSIPHON) M£LL,SI, new species 



Plate 36, Figxjre 14 



Shell elongate-conic, flesh-colored, with rather broad interrupted spiral 

 bands of brown; the elements composing these bands are arranged in 

 both axial and spiral series. Nuclear whorls decollated in our specimens. 

 Postnuclear whorls strongly rounded, narrowly shouldered at the sum- 

 mit, and marked by rather strong, retractively slanting axial ribs, of 

 which 70 occur on the first of the remaining turns in the type, 80 on 

 the second, and 94 on the last. Most of these ribs extend prominently to 

 the summit, where they form slender hollow cusps. The spiral sculp- 

 ture is poorly developed on the first of the remaining postnuclear turns; 

 on the second 8 low threads are present, and on the last 12 occur between 

 the summit and periphery. These threads render the little riblets slightly 

 wavy. Suture strongly constricted, somewhat channeled. Periphery in- 

 flated, strongly rounded. Base short, well rounded, openly umbilicated and 

 marked by the continuation of the axial ribs and six spiral threads, 

 while within the umbilicus four or more additional threads are apparent. 

 The last whorl is solute for about one- fourth of a turn. Aperture broadly 

 oval, almost circular; peristome double, a little wider on the inner lip 

 than the outer, forming a conspicuous auricle, which is rendered irregu- 

 lar by the siphon immediately behind it at the posterior angle of the 

 aperture ; inner peristome somewhat exserted and slightly reflected. Oper- 

 culum typically opisthosiphonid. 



