Occasional Papers of the Museum of Zoology 97 



honairensis. Sculpture of later whorls: growth-riblets low, 

 irregularly-spaced, often almost obsolete on last whorl; the 

 calluses often obliterate the interspaces and may be decorated 

 with faint, spiral thickenings; basal angulation slightly more 

 prominent than in honairensis. Aperture : subcircular. Other- 

 wise as in honairensis. 



Measurements 

 Shell Aperture "Whorls 



alt. maj. diam. alt. diam. 



Type, fig. 75 (C5c) 8.20 37(3.02) 22(1.84) 109(2.01) IO14 



Fig. 76 (C17) 7.20 37(2.66) 23(1.64) 108(1.76) 9^^ 



The radula of this form has been described and figured in 

 a former paper (1923; op. cit., fig. 1-5). As indicated, it ap- 

 pears closest to that of M. pontificus, but it differs from the 

 radulae of the more northern species in its simply unicuspid 

 central. The 105 transverse rows are almost straight. 



Typical curacoanus (Table IX, C5) is distributed through- 

 out the limestone portions of central and southern Curasao 

 (Cl-7, 11, 12). In the more northern localities (C13, 17, 20), 

 it is represented by a smaller form (Table IX, C17 ; fig. xvii- 

 76) with slightly more regular growth sculpture. 



Microceramus honairensis arubanus, new subspecies 



Type locality: (A4b) top of Seroe Canashito, Aruba. 



Distribution: Aruba; under limestone rocks (A2-5). 



Shell (fig. xvii-77) : more elongate than curacoanus. Color: 

 lighter and more translucent, calluses less conspicuous than 

 in preceding. Whorls : about 103^4 ; more convex and with 

 better impressed suture than either of the other subspecies. 

 Sculpture of last whorl : growth-riblets more regular than in 

 curacoanus but much lower and more rounded than in honair- 

 ensis ; calluses thin but widespread, usually with several spiral 

 thickenings; basal angulation more noticeable than in the 

 other subspecies. Otherwise as in curacoanus. 



This (Table IX, A4) is the largest form of the species, and 

 also develops the greatest number of whorls. Its sculpture 



