350 PROCEEDINGS OF THE ACADEMY OF [April, 



P. gatunensis, but in gabbi the aperture is shorter and wider, in conse- 

 quence of the more swollen last whorl. 



The embryonic shell consists of two smooth, rounded whorls; then 

 narrow, widely spaced protractive riblets, and a spiral carina at the 

 lower third, appear, for a half-whorl, giving place then to rounded 

 vertical ribs about equal to their intervals, and spiral cords passing- 

 over ribs and intervals, the spaces between them spirally striate. On 

 the last whorl there are 13 narrow spiral cords above the siphonal 

 fasciole, which is bounded above by an acute ridge. The cords are 

 enlarged where they pass over the longitudinal ribs, and in each 

 interval there are several spiral striae except in the subperipheral region, 

 where each interval has one spiral thread. On the convex siphonal 

 fasciole there are 4 to 6 small cords. Adult shells have 19 to 25 

 longitudinal ribs on the last whorl. On the preceding whorl the 

 number is diminished by about a fourth. There is no varix behind 

 the outer lip, but the ribs become obsolete there in fully adult shells. 

 The aperture is narrow and long, the outer lip strongly lirate within. 

 The columella bears, at the origin of the anterior canal, a strong, obtuse, 

 spirally entering plait, which ascends the internal column. 



Length 32^, diam. 15 mm. 

 " 30, " 14 " 

 ■ " 25, " 12 " 



There is rather wide variation in the number of longitudinal ribs, 

 while the number of major spirals remains very constant — thirteen 

 on the last whorl, the upper one being more or less obviously doubled. 

 Phos subsemicostatus n. sp. PL XXV, %. 3. 



This species is closely related to Phos semicostatus Gabb, of the 

 Santo Domingo beds. It differs by having slightly narrower more 

 numerous spiral threads, and by lacking small longitudinal riblets 

 between the rare, varix-like ribs of the later whorls. It is also larger. 



Length 42, diam. 19 mm.; 10 whorls. 



Further material may perhaps show this to be a subspecies of the 

 Santo Domingan form. Our type has lost a large part of the shell 

 from the last two whorls. 



Phos metuloides DalL 



Phos metuloides Dall, Proc. U. S. Nat. Mus., XIX, p. 303, PL 28, fig. 15 

 (Ponton, Santo Domingo; Monkey Hill, Isthmus of Panama). 



Several young specimens from Gatim show the embryonic and early 



neanic whorls. There is an embryo of at least 3 smooth whorls; 



then appear about five spiral threads crossed by very slender, widely 



spaced, protractive ribs. These gradually change, in the first sculp- 



