290 PECT1N1DA\ 



LiROPECTEN, Con., 1867. (Lyropecten, Conrad.) Somewhat 

 inequivalve, with moderately developed unequal ears, valves 

 ornamented with strong nodulose and striated ribs, near the 

 umbones always somewhat irreofularly gibbose ; hinge with a 

 few oblique teeth on each side of the ligamental fosset. Type, 

 P. nodosus, Linn, (cxxxiii, 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. seplemplicatus, 

 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 striae, 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. (S3^ncyclonema, Meek, 1864.) 

 Shell fan-shaped, thin, subequivalve ; smooth, or striate, or with 

 a few large, rounded ribs. P. pseudamussium, Lam. (cxxxiii, 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. (cxxxiii, 19). 



PSEUDOPECTEN, Bayle, 1879. Lias; Europe. P. aeqidvalvis, 

 Lam. 



VOL A, Klein, 1753. ^Janira, Schum., 1817.) Lower valve 

 convex, with produced large beaks, upper valve plane or slightly 

 concave, and frequently smaller than the lower one. P. dentatus, 

 Sowb. (cxxxiii, 20). P. atavus, d'Orb. (cxxxii, 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. aequicostatus, Lam. 

 (cxxxii, 100, 1). 



Hemipecten, Adams and Reeves, 1848. 



Distr.—l sp. Sooloo Ai'chipelago. Fossil ; Jurassic. H. 

 Forbesianus, A. and R. (cxxxiii, 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 



