6 PEOCEEDINGS OF THE NATIONAL MUSEUM. vol.64. 



Shell attaining a large size, heavy, ovate in outline, circular in 

 cross section; apex conical or hemispherical, apical angle 85° to 

 115°; early whorls bearing an indeterminate number of low swollen 

 varices (see pi. 2, figs. 3, 5) ; spire concealed at about beginning 

 of seventh whorl; callus between succeeding whorls, as shown in 

 axial section, thick at and below shoulder, rapidly thinning above 

 shoulder; inner lip bearing a heav;\' subsutural callus; outer lip 

 greatly thickened opposite this callus; channel between callus and 

 thickened outer lip very narrow and deep on body whorl, filled with 

 callus on earlier whorls ; later whorls sculptured on and below shoul- 

 der with narrow, closely spaced spiral threads; base of body of 

 young shells sculptured with narrow spiral grooves; base of outer 

 lip and base of columella of adult shell not known. 



The dimensions in millimeters of the most perfect specimens from 

 the Republic of Haiti are as follows : 



Height. Diameter. 



155 95 (pi. 1, fig. 9) 



150 110 



145 90 



115 64 



55 40 (cast, pi. 1, fig. 1) 



28 15 (pL 2, fig. 3) 



The circular cross section, the shape of the whorls, of the callus 

 between the whorls, and of the body cavity, as shown by axial sec- 

 tions, are the most characteristic features of O. aguadillensis. 

 Cooke's method of studying axial sections is particularly useful in 

 determining features of this species. The heavy subsutural callus 

 and thickened outer lip are striking features. (See pi. 1, figs. 5, 8.) 

 The deep narrow channel between them resembles the similar chan- 

 nel on Stronihus lacinatus Chemnitz, Strombus latissimus Linnaeus, 

 and other Indo-Pacific strombs that have the outer lip extending far 

 up the spire. This deep channel is shown in casts by the sharp upper 

 edge of the cast of the body whorl. The upper edge of casts of the 

 whorls of the spire are progressively blunter toward the apex. As 

 casts of different size show these features, and as shells of different 

 size have the heavy subsutural callus, the deep channel at the 

 posterior end of the body cavity is filled up as the animal withdraws 

 during growth and the subsutural callus is absorbed. The filling of 

 the channel by callus is shown in axial sections of the shell. The 

 open space in the axial sections and the corresponding parts filled 

 with sediment shown on Plate 1, Figures 3, 4, 10, 11, correspond to 

 the casts (pi, 1, figs. 1, 6, 7). The range in outline of the shell isl 

 shown by Plate 1, Figures 4, 10, which represent two worn specimens 

 from the same locality. As Cooke observed a similar difference in 



