MUSEUM OF COMPARATIVE ZOOLOGY. 219 



Pecten eflQuens, n. s. 



Shell small, high, flattened, covered all over with very fine striae radiating 

 from the umbo, but diverging from the middle line of the valve without refer- 

 ence to the other sculpture; left valve with about ten Little elevated poorly 

 defined ribs, which are most distinct in the young, rounded, smooth, separated 

 by wider shallow interspaces, in which are from three to seven minute sub- 

 equal regular threads, with small hardly elevated, regularly spaced, transverse 

 scales on them ; anterior ear very small, obliquely cut off; posterior ear high, 

 short, with about ten obscure radiating threads ; cardinal margin straight, 

 simple ; right valve ^ith faint radiating ridges most prominent near the mar- 

 gin, and tending to pair ; ears similar to those of the opposite valve, byssal 

 notch small, fasciole very narrow, with four pectinium-spines beyond the edge 

 of the ear, and a series of them overhanging the fasciole within it ; cartilage 

 pit rather small, inner cardinal border nearly smooth ; color pale orange. 

 lemon-yellow toward the umbo ; height of largest valve, 26.0. width 22.0 mm.; 

 umbonal angle about 85°. 



Valves were dredged in 127 fms. off Havana, by Sigsbee. 



This shell seems nearest P./urtivus Loven, but has smaller anterior ears, 

 finer strite, and altogether different coarse sculpture, especially on the left 

 valve. Both forms have the Camptonectes striation. 



Section PSEUDAMUSIUM H. & A. Adams. 



" Pseudamusium Klein, Tent. Meth. Ostracol., p. 134, 1753." Stoliczka, Pal. Indica, 



Cret. Pelec, III. p. 426, 1871. 

 Pseudamussium H. & A. Adams, Gen Rec. Moll., II. p. 553, 1858 (no type mentioned). 



Chenu, Man. de Conchyl., II. p. 184, 1862; P. dispar. Jeffreys, 



Ann. & Mag. Nat. Hist., Nov. 1876, p. 424. 

 Syncydonema Meek, Cret. & Jur. Foss. Smithsonian Check List, 1864, p. 31 ; P. rigida 



H. & M. Stoliczka, 1. c, p. 426, 1871. 



Shell thin, smooth or delicately sculptured, small; valves subequal, closed 

 except at the byssal foramen; ears unequal, the posterior ones often hardly 

 differentiated from the body of the shell; hinge line straight ; notch distinct; 

 margin entire; interior destitute of radiating ribs; shell free, byssiferous. 

 Types Pecten dispar and P. pseudamussium Lam. 



The name Pseudamusium is due to Klein, but was first introduced into 

 regular nomenclature and defined by H. & A. Adams, who, however, did not 

 name a type, an omission which was supjdied by Chenu. There do not ap- 

 pear to be any sound characters by which Sxjncydonema can be differentiated 

 from the other species here included, and it is very probable that Camptonectes 

 (Agassiz Ms.) Meek, 1864, and its synonym Ehurneopecten Conrad, 1867, should 

 also be combined with it. These species, however, have a somewhat peculiar 



