290 PECTINIDA. 
LIROPECTEN, Con., 1867. (yropecten, Conrad.) Somewhat 
inequivalve, with moderately developed unequal ears, valves 
ornamented with strong nodulose and striated ribs, near the 
umbones always somewhat irregularly gibbose; hinge with a 
few oblique teeth on each side of the ligamental fosset. Type, 
P. nodosus, Linn. (exxxiii, 17). There are a few tertiary species 
from North America referred to this subgenus, and it is very 
likely also that species, like the cretaceous P. septemplicatus, 
Nilss., and a few others, belong to it. 
CAMPTONECTES, Agassiz, 1864. (Eburneopecten, Agass., 1865.) 
Valves subequal, moderately flattened, ovate or subovate, with 
well-developed, or rather small, unequal ears, the anterior of 
the right valve with a byssal sinus, surface marked with fine 
radiating, curved striz, separated by punctated grooves. Type, 
P. lens, Sow. Forms belonging to this subgenus only occur in 
the mesozoic strata. The two valves often are unequally 
strongly striated. 
PSEUDAMUSSIUM, Klein, 1753. (Syneyclonema, Meek, 1864.) 
Shell fan-shaped, thin, subequivalve ; smooth, or striate, or with 
a few large, rounded ribs. P. pseudamussium, Lam. (exxxiii, 18). 
PLEURONECTIA, Swainson, 1840. (Amussium, Klein, 1753.) 
Shell nearly orbicular, depressed, subequivalve, with very small 
ears ; smooth outside, with radiating ribs inside. Large species, 
with the peculiarity that one valve is highly colored, the other 
white. The group is almost sufficiently distinct from Pecten to 
merit the generic position given it by several systematists. P. 
Japonicus, Gmel. (exxxili, 19). 
PSEUDOPECTEN, Bayle, 1879. Lias; Europe. P. xquivalvis, 
Lam. 
voLA, Klein, 1753. (Janira, Schum., 1817.) Lower valve 
convex, with produced large beaks, upper valve plane or slightly 
coneave, and frequently smaller than the lower one. P. dentatus, 
Sowb. (exxxiii, 20). P. atavus, d’Orb. (exxxii, 99). 
NEITHEA, Drouet, 1824. Shell inequivalve, like Vola, but with 
obscure cardinal teeth on the sides of the cartilage-pit, and tooth- 
like folds on the wings. Fossil only. P. equicostatus, Lam. 
(exxxit 100, 1). 
Hemipecten, Adams and Reeves, 1848. 
Distr.—1 sp. Sooloo Archipelago. Fossil; Jurassic. 4. 
Forbesianus, A. and R. (exxxiii, 21). 
Shell inequivalve, irregular, more or less transparent; upper 
valve auricled, with a slit below the ear, with denticulated mar- 
gin; hinge toothless; ligament marginal, in a small central pit. 
H. Forbesianus, Ad. and Reeve, is the only recent species 
known. It appears to adhere temporarily by the right flat- 
tened valve to submarine objects; its thin hyaline structure is 
