92 BUIXETIN 29 256 



Shell closely resembling the recent A. ambigua, which 

 abounds on the beach at Monte Cristi ; but differing in the fol- 

 lowing respects: — (1) The perfect fossil shells have an elevated, 

 conical protoconch of three to three and one-half smooth whorls, 

 the apical very small, the others gradually increasing; while the 

 recent shells all have a broad protoconch formed of one and one- 

 half to two smooth, flattened, and noticeably swollen whorls; (2) 

 the fossil shells have fourteen ribs on the last whorl, the recent 

 only twelve; (3) the fossil shells are smaller, our largest recent 

 shell measures 12X7, but the largest fossil is only 8X5 mm. 



I would think the fossil shell a dwarfed form of the recent 

 were it not for the striking difference in the protoconchs, sug- 

 gesting that they were derived from diverse ancestral stocks. 



Dr. Dall listed A. ambigua from Bow r den, Jamaica, and from 

 Santo Domingo. Probably the Dominican, and perhaps the 

 Bowden forms are the same as ours. 



The Gatun species A. prceambigua Brown and Pilsbry differs 

 from our shell widely in its spiral sculpture, the spirals being 

 spaced instead of closely crowded as in the Dominican shell, 

 which has twenty as against eight on the last whorl above the 

 sulcus, and seven against three on the penultimate whorl. The 

 Gatun species also has fewer nuclear volutions. 



Locality. — ■ (Exp'd '16) Zone D, Rio Gurabo at Los 

 Quemados. 



Genus Tritia Risso 



Tritia golfoyaquensis, n. sp. 



Plate 15, Figures 24, 25 



Shell with an elevated acute spire, suture distinct; whorls 

 seven, convex, surface ornamented with very regular, flat spiral 

 ridges (eight on the penultimate whorl) sub -cancellated by much 

 feebler longitudinal growth-lines ; aperture wide, oval; anterior 

 sinus deep; outer lip sharply striate internally; inner lip with a 

 posterior callus; canal twisted. Length 17, width 9 mm. 



Locality. — (Exp'd '16) Bluff 3, Cercado de Mao. 



