MOLLXJSCA OF PORTO RICO. 
427 
Section ELACHISTA Dali, 1901, 
This small group of forms, which seem referable to Bittium, was referred by Carpenter to the 
Styliferina of A. Adams, and the senior author of this paper followed this usage in several of his 
papers without investigation, a course which proves to be incorrect. It seems that each fauna in 
America, either recent or fossil, Atlantic or Pacific, in the warm-temperate or tropic /.one, from the 
Oligocene to the present day, contains two or more forms of this sort, and the Bittium elachistum of 
the Paris Basin Eocene, described by Cossmann, would appear, from his figures, to belong here. These 
shells are characterized by their minute pupoid form, the axial sculpture faint and more or less 
confined to the apical portion, the aperture with hardly a trace of canal or varix. The type may 
betaken as B. cerithidioide Dali (Trans. Wagner Inst., nr, p. 276, pi. xvr, fig. 8, 1892). It may be 
mentioned that this figure is of an immature shell, in which the basal angle is much sharper than in 
the adult. 
Bittium cerithidioide Dali. 
? A laba ceritliidioidea Dali, Blake Report, II, p. 258, 1889; Trans. Wagner Inst., in, p. 27 (> , pi. xvi, fig. 8, 1892. 
Shell with nine or ten whorls, the first three smooth and increasing slightly, the next three 
carinated below the middle, the lower whorls rounded, those below the fourth generally having 
delicate, curved, longitudinal ribs; the base is sculptured with faint revolving grooves; aperture 
somewhat rounded; columella feebly curved and ending in a slight lip below, behind which is a 
small umbilical chink; outer lip not thickened. Color brownish. 
Length, 3.5; diameter, 1.25 mm. 
Mayaguez, Porto Rico, six worn and broken shells. 
The shells have a strong resemblance to a minute Cerilhidea before the lip has become thickened 
and reflexed. 
Family MODULI DAi. 
Genus MODULUS Gray, 1840. 
Shell perforate, lenticular, turbinate, or trochiform, porcellanous, solid, sculptured; aperture 
rounded; columella arcuate, ending at its base in a sharp tooth; operculum oval to rounded, 
multispiral, its nucleus subcentral. 
Modulus modulus Linnaeus. 
Trochus modulus Linnaeus, Syst. Nat., ed. x, p. 757, 1758. 
Modulus lenticulnris Tryon, Man., IX, p. 261, pi. XLVIII, figs. 91, 92, 1887. 
Shell solid, lenticular, with a low, rather sharp-pointed spire and a decided peripheral keel, the 
last whorl decidedly descending at the aperture; upper surface sculptured with low, revolving ridges 
and a series of rather strong radiating ribs; on the base there are from five to eight strong revolving 
ridges separated by deep grooves; lips strongly ridged within; basal tooth of the columella horizontally 
compressed. Color white with small brown spots; on the base the spots occur on the ribs. 
Height, 10; diameter, 13 mm. 
Boqueron Bay, off Ilumacao; Fajardo; Guanica; Ponce; Arroyo; Cabo Rojo light; Mavaguez; 
Puerto Real, Porto Rico; Ensenada Honda, Culebra; Vieques. 
In the type the whorls are nearly flat above; in the variety Jtoridanus they are somewhat 
convex and radiately ribbed. 
Modulus catenulatus Philippi. 
Trochus ccitenulatus Philippi, Chemnitz Conch. Cab. neue Ausgabe, Trochus , p. 110, pi. xvm, fig. 4, 1851. 
Shell trochiform, solid, with a rather high, sharp-pointed spire and flat or slightly concave 
whorls, the last not descending at the aperture, with a very sharp peripheral keel; base inflated, but 
somewhat excavated around the small umbilicus, sculptured above and below with rather fine, 
revolving cords, which are made subnodulous by the crossing of the growth lines; basal tooth sharp, 
compressed; below it the basal edge of the shell is excavated. Color grayish or brownish, with white 
dots on the ribs, the base whitish. 
Height, 15; diameter, 15 mm. 
San Juan, Porto Rico, three worn shells. 
The species is abundant on the west coast of tropical America from Panama northward. 
