294 ANOMIIDA. 
Behring’s Sea, Ochotsk; 50 fathoms. Miocene; California. P. 
macrochisma, Desh. (exxxi 76). 
Shell adherent, subequivalve, irregular, flattened ; hinge with 
two thick, divergent elongated lamella in the inferior, corres- 
ponding with two long pits in the upper valve ; upper valve with 
only two muscular impressions; the pedal scar radiately striated ; 
the byssal plug is often fixed in the lower valve, and its muscle 
becomes (functionally) an adductor. 
PODODESMUS, Philippi, 1849. Valves radiately grooved ; per- 
foration of lower valve moderate, firmly embracing and enclosing 
the plug. P. rudis, Brod. (exxxi, 77). 
MONIA, Gray, 1849. Valves radiately grooved ; perforation of 
lower valve large, only slightly embracing the large, thin, plug. 
P. Zealandica, Gray (exxxiii, 26). 
PARANOMIA, Conrad, 1860. Irregular, inequivalve, one valve 
flattened or slightly concave, hinge of lower valve with a broad, 
irregular, triangular tooth or plate, flattened or slightly convex, 
with sharp margins and an anterior, compressed, small, but 
prominent tooth; muscular impression situated toward the 
ventral margin in a line with the apex, or nearly equidistant 
from the anterior and posterior ends. Type, Placunanomia 
Saffordi, Con., from cretaceous rocks of Tennessee. There are 
only two other cretaceous species which Conrad refers to the 
same group; it seems to be closely allied to Philippi’s Podo- 
desmus. The convex valve has no teeth or appendage, and is 
generally radiately ribbed; the flatter valve is often attached 
near the umbo to other objects and very thin, but not perforated. 
CYcLOSTREON, Eichwald, 1867. 
Distr.—Fossil. Cret., Eocene; sBiacapes 
Shell obliquely ovate, with attenuated obtuse beaks, inequi- 
valve ; one (right 7) valve convex; the other (left ?) smaller, flat 
or concave, with a small transverse ligamental groove at the 
apex; in the convex valve there is only a small lateral groove 
below the beak, placed somewhat anteriorly ; both beaks are 
truncate and appear to indicate an attachment to foreign bodies; 
muscular impression indistinct, represented by a marginal zone 
which surrounds the cavity of the convex valve. The type 
greatly resembles Hemiplicatula, but is stated to have no such 
hinge or cartilage ribs as are characteristic of that genus. 
ANOMIANELLA, Ryckholt, 1852. 
Distr.—A. proteus, Ryck. (cxxxii, 12). Carboniferous; 
Belgium. 
Shell ovate, thin, found attached to other shells ; there appears 
to be no perforation in the lower valve. 
