BULLETIN OF THE UNITED STATES FISH COMMISSION. 
466 
scabrous ribs. Color whitish yellow, orange, reddish, or purplish; sometimes uniform in coloring, often 
beautifully maculated with red, purple, or brown. 
Length, 20; height, 23; diameter, 8 mm. Mavaguez, Porto Rico, a number of young valves. 
A beautiful and variable little species, with an infinite variety of coloring. The valves are 
sometimes made quite rough by the sharp scales on the ribs. 
Pecten lemniscatus Reeve. 
Pcctrn lemniscatus Reeve, Conch. Icon., vm, pi. xxxv, fig. 170 (see Errata), 1853. 
Shell elevated, thin, somewhat fan-shaped, compressed, nearly equivalve and equilateral, with 
small, slopingly cut posterior and large, projecting anterior ears, that of the right valve with a 
large, deep, byssal notch; surface sculptured with numerous, rather low, unequal ribs and riblets, the 
principal ones sharply and often strongly scaly; valves with a well-defined radiating shoulder below 
the ears and ridged on the interior to correspond with the external sculpture; ears with small, feeble 
ribs, which are roughly scaly. Color very variable, much as in P. ornatus, but not so distinctly marked. 
Length, 35; height, 40; diameter, 10 mm. 
San Juan Harbor, Porto Rico, one young valve. 
This species is close to P. onuitas, but differs in the ribs, which are rather low and are never 
separated by deep, excavated grooves. The color pattern is generally less distinct. P. effluens Dali is 
probably the same species, though P. lemniscatus is also found in Mauritius. The sculpture of the 
lower valve is generally more feeble than that on the upper valve. 
Pecten sp. 
A single right valve was obtained in Mavaguez Harbor of a form which seems to approach P. 
darwini, but is probably undescribed. The specimen is too young and imperfect to be described. 
Pecten exasperatus Sowerbv. 
Pecten exasperatus Sou crby, Thes. Conch., p. 54, pi. xvm, figs. 183-186, 1816. 
San Juan, Porto Rico (Gundlach). 
Pecten antillarum Recluz. 
Pecten antillarum Rccluz, Joum. do Conchyl., iv, p. 53, pi. v, fig. 1, 1853. 
San Juan, Porto Rico (Gundlach). 
Subgenus Amusium Bolten, 1798. 
Section PROPE AMTJSITTM De Gregorio, 1883. 
Pecten nanus Verrill & Bush. 
Cyclopeclen nanus Verrill <k Bush, Trans. Conn. Acad. Sci.,x, pp. 85, 92, pi. xvi, figs. 12-12c, 1897. 
Shell very small, nearly orbicular, compressed, subequivalve, equilateral, with rather small, 
nearly equal ears; surface apparently smooth, but generally (in adult shells) seen to be sculptured 
with very fine, close riblets; in other specimens the sculpture consists of microscopic, concentric strife; 
ears generally having delicate, radial sculpture, the anterior one on the right valve sometimes slightly 
cancellated; within there are generally exceedingly faint radial ridges. Color semitransparent whitish 
or horny, often clouded, mottled, or irregularly rayed with milky white. 
Length, 5.5; height, 5.5; diameter, 1.75 min. 
Mavaguez, Porto Rico, many partly worn valves. 
Pecten pourtalesianum Dali. 
Pecten ( Pi -opcamu's turn ) pourlalesianam Dali, Blake Report, i, p. 211, pi. iv, fig. 3, v, fig. 12, 1886. 
8hell small, thin, compressed, suborbicular, with small, nearly even ears; right valve with well- 
developed concentric ridges; the left appearing smooth, but having microscopic, concentric lines and 
radiating riblets; within there are from nine to eleven slender, somewhat club-shaped, radiating ribs 
in each valve which do not extend to edge of shell. Color generally milky white and subtranslucent, 
the ribs showing through, but sometimes brownish or reddish brown and dotted with white. 
Length, 13; height, 13; diameter, 2.5 mm. 
There was a single specimen and a left valve obtained at Mavaguez Harbor of the var. striatulum 
Dali. (See Blake Report, i, p. 212.) 
As in other allied species, the light valve is not completely calcified near the border and it 
collapses just outside of the ribs, so that its outer portion lies in contact with the left valve. 
