434 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Rissoina chesnelii Michaud. 
/ lissoa chesnelii Michaud, Desc. des Coq. Nouv., p. 17, 1832. 
Rissoina chesneli Schwartz v. Mohr., Mon. Rissoina, p. 73, pi. v, figs. 38, 39, 1860. 
Shell white, with eight somewhat rounded whorls, having about fourteen strong, longitudinal 
costae with about equal interspaces which are scarcely spirally striate; columellar callus solid, elevated. 
There is a revolving oblique ridge at the base of the shell. Length, 4; diameter, 1.5 mm. 
Mayaguez, Porto Rico; a fragment. 
Rissoina cancellata Philippi. 
Rissoina cancellata Philippi, Zeits. fur Mai., 1847, p. 127; Schwartz v. Mohr., Mon. Rissoina, p. 89, pi. vii, fig. 52, 1860. 
Shell white, with ten convex whorls which are cancellated with sixteen to eighteen longitudinal 
ribs and four or five revolving ridges; revolving ridges on the base numerous; outer lip strong; basal 
notch well developed. There is a faint revolving rib at the base of the shell. Length, 8; diameter, 3 mm. 
Mayaguez, Porto Rico; Vieques. 
Subfamily HYDROBIIN.®. 
Genus POTAMOPYRGUS Stimpson, 1865. 
Potamopyrgus coronatus Pfeiffer. 
Paludina coronata Pfeiffer, Arch, fur Naturg., I, 1840, p. 253. 
Amnicola coronata Fischer & Crosse, Mission Sci. Mexique, pt. vii, vol. ii, p. 266, pi. l, figs. 6 a-e, 1891. 
Several localities in Porto Rico; Vieques; Cuba, and other localities in the West Indies (Fischer 
& Crosse); Texas; Mexico; Central America; Colombia; Venezuela, etc. 
The variety crystallinus Shuttleworth is also reported from Porto Rico. 
Family CYCLOPHORID^. 
Shell variable in form, turbinate, turriculated, or subdiscoidal; aperture rounded; peristome 
simple or reflexed; operculum circular; jaw formed of two triangular pieces. 
Genus MEGALOMASTOMA Guilding, 1840. 
Shell perforate, elongate, turriculate, or pupiform; apex generally decollated; aperture subcircular; 
peristome continuous; operculum horny, circular, flat, arctispiral, with a central nucleus. 
Type, Megalomastoma antillarum Sowerby. 
Megalomastoma croceum Gmelin. Plate 53, fig. 1. 
Helix crocea Gmelin, Syst. Nat., p.3655, 1792; Chemnitz, Coneh. Cab., ix, pi. 135, fig. 1233, 
Megalomastoma cylindraceum Sowerby, Conch. Icon., xx, pi. x, fig. 91, 1878. 
Shell elongated, subcylindrical, with fine, oblique, flexuous strife, which, with the epidermis, 
are usually eroded away; whorls remaining from six to eight, scarcely convex, the first one to one and 
a half decollated; aperture nearly circular; peristome continuous, appressedto the last whorl, but. little 
thickened, slightly reflexed; umbilicus a mere chink. The surface, where not eroded, is generally horn 
colored, but ordinarily it is a dirty white or reddish ash. Sometimes the last whorl or two are flushed 
with reddish brown or violet. 
Length, 30; diameter, 12; length of aperture, 7 mm. 
El Yunque, Porto Rico; several dead specimens. 
Megalomastoma croceum var. curtum Dali A Simpson., Plate 53, fig. 2. 
A small variety, having only six remaining whorls, was found at Hucares, Porto Rico. 
Length, 21; diameter, 10 mm. 
Megalomastoma hjalmarsoni Pfeiffer. 
Megalomastoma hjahnarsoni Pfeiffer, Mal.Blatt., xxu, p. 119, 1875. 
Lares; Mayaguez, western Porto Rico (Crosse). 
Megalomastoma verruculosum Shuttleworth. 
Cyclostoma (Megalomastoma) verruculosum Shuttleworth, Diagn.neue Moll., Berner Mitth., 1854, p. 90. 
Eastern Porto Rico (Crosse). 
