228 NEW-YORK FAUNA — MOLLUSCA. 
PETRICOLA PHOLADIFORMIS. 
PLATE XXVIII. FIG. 262. 
(STATE COLLECTION.) 
Petricola pholadiformis. Lam. An. sans vert. Vol. 5, p. 505. Ed. prior. 
P. fornicata, Say, Jour. Acad. Nat. Sciences, Vol. 2, p. 319. 
iP: pholadiformis. Ip. Am. Conchology, pl. 60, fig. 1. Russet, Ess, Jour. Vol. 1, p, 55. 
iP. id. Conrap, Amer. Marine Conchology, p. 37, pl. 7. 
P. id. Gouxp, Invertebrata of Mass. p. 63. 
Description. Shell very much elongated transversely, with the beaks near the anterior end, 
inflated, cylindrical, equivalve. Anterior margin acutely rounded ; the posterior margin 
obtusely rounded and slightly gaping. Hinge and basal margins nearly straight, almost 
parallel. Beaks elevated, with an ovate area in front, which is well defined. Surface coarsely 
marked with elevated lines, more or less conspicuous, radiating from the umbones, and most 
prominent on the anterior part of the shell; the surface is also coarsely marked by the lines 
of growth, which, on the radiating ribs, assume the form of tooth-like scales or spines. Teeth 
two in each valve, appearing to rise out of the cavity of the beaks, and curving upwards: in 
one valve, the anterior tooth distinct and grooved ; the other in front, short. In the other valve 
is a large tooth, so deeply divided as to appear like two, and behind it a smaller, thin and 
divergent tooth. Interior surface impressed by the external radiating ridges. 
Color, greyish brown; the dead shells chalky white. 
Vertical axis, 0*6; transverse ditto, 1°7. 
This species occurs along the coast of Long island, imbedded in ooze and the sedgy banks 
of creeks. The dead shells are frequently found along the coast. On account of the exces- 
sive delicacy of the teeth, it is rare to obtain perfect specimens. 
PETRICOLA DACTYLUS. 
PLATE 28. FIG. 283. a 3. 
Petricola dactylus. Sowersy, Genera, pl. 3. 
P. id. Say, American Conchology, pl. 60, fig. 2. 
P. id. GouLp, Invertebrata of Mass. p. 65, fig. 41. 
Description. Shell transversely oblong-oval, inflated. Basal margin curved; edges of the 
anterior margin everted: no distinct area before the beaks, which are prominent. Surface 
with numerous radiating raised ridges, which are not scaly as in the preceding; about 15 - 
18 of these on the anterior portion are large and distinct, the remainder are filiform: the 
stages of growth marked by undulated lines. ‘Two teeth in the right valve, and two in the 
other, of which one is bifid. 
Color. Soiled brownish white. 
Vertical axis, 0:7; transverse ditto, 1°5 — 2°0. 
