470 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Section MODIOLUS s. s. 
Modiolus tulipus Lamarck 
Moil ini a tulipa Lamarck, An. sans Vert., vr, p. Ill, 1819; Reeve, Conch. Icon., x, pi. iv, fig. 15, 1857. 
Shell subtrapezoidal, somewhat elongated, inflated, subsolid, with a faint posterior wing; a nearly 
straight rounded posterior ridge runs from the beaks to the posterior base of the shell; in front of this 
ridge the base is slightly incurved; epidermis somewhat concentrically striate, covered with a scaly 
growth, which develops into bristly hairs that part near the byssus, smooth. There is generally a broad 
reddish stripe on the posterior ridge, with a lighter one in front of it, though this area and the 
posterior part may be radiately banded red and white in narrow streaks. The anterior part of the 
shell is often a chestnut or burnt brown. 
Length, 85; height, 40; diameter, 40 nun. 
San Juan; Boca Prieta; Mayaguez Harbor, Porto Rico. 
Section AMYGDALTJM Megerle, 1811. 
Modiolus arborescens Dillwvn. 
Mytilus arborescens Dillwvn, Descr. Catalogue Rec. Shells, i, p. 306, 1X17. 
MnrUola arborescens Reeve, Conch. Icon., ,\, 1857, pi. VI, fig. 30. 
Shell very thin, slightly inflated, long-obovate, smooth except for faint growth lines, brilliant; 
beaks low; posterior ridge scarcely developed. Color pale straw or ashy, lighter on the posterior ridge, 
the posterior slope being beautifully marked with arborescent, blackish lines. Sometimes this area is 
marked so that the dark lines inclose various-sized, triangular spots of the color of the shell. 
Length, 50; height, 20; diameter, 13 mm. 
Mayaguez; San Juan, Porto Rico. 
An exceedingly delicate and beautiful species. 
Section BOTULA Morch, 1853. 
Modiolus cinnamomeus Lamarck. 
Mi/tilus cinnamomeus, etc., Chemnitz, Conch. Cab., vm, p. 152, pi. lxxxii, fig. 371, 3785. 
Mml-ioln cinnamomea Lamarck, An. sans Vert., Vi, p. 114, 1819. 
Shell small, nearly smooth, subrhomboidally and somewhat elongated, slightly arcuate, inflated, 
with a thick, dark chestnut epidermis, which shows distinct, often dark, rest periods, and is darker 
colored at the posterior end and anterior base; beaks full and high, placed at the upper anterior 
extremity of the shell and projecting in front of the anterior end; hinge line curved, the line 
extending around to the anterior base in an unbroken curve. 
Length, 10; height, 5; diameter, 6 mm. 
Mayaguez Harbor, Porto Rico, one shell. 
Section GREGARIELLA Monterosato, 1884. 
Modiolus eoralliophagus Gmelin. 
Mt/lilm coralliophagus Gmelin, Svst. Nat., p. 3359, 1792. 
Shell small, oblong, much inflated, varying much in form, generally higher and more inflated in 
front, with a high posterior ridge, from which radiating stria; curve backward and downward, those 
on the posterior slope stronger, crossed by heavy growth lines and subnodulous, those in front of the 
ridge line and unbroken; from the beaks to about the center of the base there is a constriction, and in 
front of this there is a space without radial sculpture but showing plainly concentric lines; at the 
rounded anterior end there are fine radiating ribs; beaks curved inward and forward, placed at the 
extreme anterior end; the inner edge’s of the shell are finely serrate. Color dirty white or brownish. 
Length, 20; height, 8; diameter, 9 mm. 
Mayaguez; Guanica; Boqueron Bay; Arroyo, Porto Rico; Ensenada Honda, Culebra. 
This species nests in coral sand and frequently has a part of the nest attached, especially at the 
posterior ridge. It is the Bofula semen of authors and the Modiola opifex of Say. 
Genus LITHOPHAGA Bolten, 1798. 
Shell cylindrical, having a thick epidermis, the low beaks placed at or near rounded anterior end; 
posterior end pointed or wedge-shaped; hinge line linear, without teeth; ligament marginal, internal. 
