MUSEUM OF COMPARATIVE ZOOLOGY. 219 
Pecten effluens, n. s. 
Shell small, high, flattened, covered all over with very fine strie 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 with 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. furtivus Lovén, but has smaller anterior ears, 
finer striz, and altogether different coarse sculpture, especially on the left 
valve. Both forms have the Camptonectes striation. 
Section PSEUDAMUSIUM H. & A. Apams. 
“ Pseudamusium Klein, Tent. Meth. Ostracol., p. 134, 1753.” Stoliczka, Pal. Indica, 
Cret. Pelec., III. p. 426, 1871. 
Pseudamussium H. & A. Adams, Gen Ree. 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. 
Syncyclonema 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 supplied by Chenu. There do not ap- 
pear to be any sound characters by which Syncyclonema can be differentiated 
from the other species here included, and it is very probable that Cumptonectes 
(Agassiz Ms.) Meek, 1864, and its synonym Eburneopecten Conrad, 1867, should 
also be combined with it. These species, however, have a somewhat peculiar 
