124 GEOLOGY AND PALEONTOLOGY OF THE WEST INDIES. 



whorl by a distinct, sometimes impressed line; callus turgid, of variable width, 

 usually concealing much of the umbilicus. 



Dimensions Alt., 38 mm.; diam., 39 mm.; length of body-whorl at aperture. 35 . 5 mm. 

 37 38.5 35.0 



53.5 55 50.5 



This species closely resembles A. amphora Heilprin, but the spire is 

 less elevated than in that species. 



Locality. The two cotypes were collected by J. W. Spencer in 

 Antigua; a larger but less perfect specimen was obtained by Vaughan 

 at the bluff on the north side of Willoughby Bay, Antigua (station 

 6881). Casts of a similar, perhaps identical, species were collected at 

 Crocus Bay, Anguilla (station 6894). 



Geologic horizon. Oligocene, Antigua formation. 



Types. U. S. Nat. Mus. No. 167031. 



Sinum chipolanum (Dall) 

 (Plate 5, Figures 6 a, &.) 



Sigaretus chipolanus Dall, Trans. Wagner Inst., vol. 3, pt. 2, p. 379, plate 17, fig. 7, 1892. 

 Sinum chipolanum Dall, U. S. Nat. Mus. Bull. 90, p. 109, plate 12, fig. 29; plate 16, fig. 1, 1915. 



The following is the original description of this species : 



"Shell solid, rather thick, varying in rotundity with age, the young ones 

 as a rule being more naticoid in shape, while the more advanced are relatively 

 flatter, and the fully mature specimens again are more rotund; whorls four or 

 five, sculptured with rather fine, flattish, revolving threads of varying size, 

 separated by channelled interspaces, varying in width and minutely undulated 

 or reticulated by the sharp, close-set, fine incremental lines; aperture large, 

 oblique; base somewhat flattened, periphery rounded; pillar lip arched, 

 broad, flattened somewhat and sometimes excavated, with a narrow sulcus 

 behind it, running up to the imperf orate umbilical region; callus on the body 

 moderate, lip not reflected. Max. Ion. of adult 33; diam. 27 mm. ; Ion. of young 

 shell 16.5; axial elevation 11; diam, 15 mm. 



"This species is most nearly related to S. declivis, from which it may be 

 separated by its closed umbilicus and the absence of the emargination of the 

 pillar, which is the most characteristic feature of declivis. It also recalls S. 

 bilix var. mississippiensis, which has a perforate umbilicus and is more rotund. 

 The sculpture may be close or sparse; it varies in this respect in nearly all 

 the species." 



The specimen from Anguilla is more depressed and much less rotund 

 than is customary for S. chipolanum, but comes well within the range 

 of variability of that species in those respects. It is very much less 

 rotund than the form from the Tampa "silex" bed, which may be 

 specifically distinct from S. chipolanum. 



The dimensions of the figured specimen are as follows: max. Ion., 

 16.9 mm.; axial elevation, 10 mm.; diam., 11 mm. 



Localities. Crocus Bay, Anguilla, station 6894, Vaughan ; also Chipola . 



Geological horizon. Oligocene. 



Type.U. S. Nat. Mus. No. 112967. 



Figured specimen U. S. Nat. Mus. No. 167033. 



