450 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
they are crossed by concentric ridges which are often nodose at the crossings; perforation keyhole- 
shaped, bounded by a black line without and a callus within that is distinctly truncated behind; inner 
edge of the shell toothed, and from the edge there are grooves running inward that mark the place of 
the ribs; white within the hole, callus sometimes bounded with a dark line; the outside of the shell is 
whitish, unicolored, or with radial dark stripes. 
Length, 35; breadth, 26; height, 15 mm. 
San Juan; San Geronimo, Porto Rico. 
Fissuridea alternata Say. 
Mssuretta alternata Say, Journ. Acad. Nat. Sci., Phila., II, p. 281, 1822. 
Glyphis alternata Pilsbry, Man., xn, p. 211, pi. xxxvn,figs. 50-53, 1800. 
Shell oval, elevated, conical; front slope straight or concave; back slope generally convex; 
surface closely sculptured by radiating ribs, of which three are small and every fourth one is larger; 
these are crossed by fine, concentric laminas which form little scales where they pass over the ribs. 
Color white, grayish, or yellowish, radiately marked with pink, brown, or black stripes which are 
often somewhat broken. The summit is in front of the middle, more or less inclined forward; opening 
keyhole-shaped, the front part of it appearing as if it had been broken away for some distance down 
the shell. Inside white; margin toothed. . 
Length, 36; breadth, 22; height, 16 mm. 
Ensenada Plonda, Culebra. 
Fissuridea alternata var. dysoni Reeve. 
Fissurella Reeve, Conch. Icon.,vi, fig. 63. 
A form with very strong, sharp sculpture and intensely black, broken, radiating stripes, which 
become brownish at the base of the shell. 
Ensenada Honda, Culebra. 
Fissuridea alternata var. sayi Dali. 
Fissurella alternata var. sayi Dali, Blake Report, ii, p, 407, 18S9. 
This form differs from the F. alternata of Say in being smaller and generally without color or 
only having a faint olivaceous tint and in having a more delicate shell. 
Mayaguez, Puerto Real, Porto Rico. 
Fissuridea variegata Sowerbv. 
j Fissurella variegata Sowerby, Thes. Conch., p. 200, figs. 172,173. 
Shell small, oblong, depressed, back slope a little rounded, front slope nearly straight, sculp- 
tured with alternating, radiate ribs and strong concentric threads; opening long, somewhat cross-shaped. 
Interior toothed at border. The ground is whitish, and there are about seven wide bottle-green or 
brownish radiating stripes which do not reach the summit, and these show through on inside of shell. 
Length, 10; breadth, 5; height, 2.5 mm. 
Mayaguez Harbor, one immature shell. 
Fissuridea viridula Lamarck. 
Fissurella viridula Lamarck, An. sans Vert., vi, p. 13, 1822. 
Glyphis viridula Pilsbry, Man., xn, p. 226, pi. lxii, figs. 22-25, 1890. 
Mayaguez; Aguadilla, Porto Rico (Gundlach). 
Genus SUBEMARGINULA Blainville, 1825. 
Shell round-oval, conical; apex near the middle, curved backward; surface radiately ribbed; 
anal notch generally short, continuing upward as a groove inside, the groove covered by a prominent 
rib outside; muscle scar horseshoe-shaped, its anterior ends recurved and pointed towards the summit 
of the shell. 
Subemarg'inula octoradiata (Gmelin) A. Adams. 
Patella octoradiata Gmelin (part), Syst. Nat.,p. 3699, 1792. 
Subeniarginula octoradiata Pilsbry, Man., XII, 273, pi. XXIX, figs. 17, 18, 37, 1890. 
Shell oval, solid, conical; apex subcentral, inclined backward and to the right; there are eight prin- 
cipal radiating ribs with smaller intermediate ones which are generally roughly nodulous. Whitish 
without, olive or brownish green, sometimes bluish within. Anterior groove narrow; border toothed. 
Length, 23; breadth, 20; height, 10 mm. San Geronimo; Ponce; Fajardo; San Juan, Porto Rico. 
