294 ANOMIID-ai. 



Beliring's Sea, Ochotsk ; 50 fathoms. Miocene ; California. P. 

 macrochiama^ Desh. (cxxxi Y6). 



Shell adherent, subequivalve, irregular, flattened ; hinge with 

 two th'ck, 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. halves radiately grooved ; per- 

 foration of lower valve moderate, firmly embracing and enclosing 

 the plug. P. rudis, Brod. (cxxxi, TT '. 



MONIA, Gray, 1849. Yalves radiately grooved; perforation of 

 lower valve large, only slightly embracing the large, thin, plug. 

 P. Zealandica^ (jsxa,y (cxxxiii, 26). 



PARANOxMiA, 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. Tj'pe, 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 

 generall}^ radiately ribbed ; the flatter valve is often attached 

 near the umbo to other objects and very thin, but not perforated. 



Cyclostreon, Eichwald, 1867. 



JDistr. — Fossil. Cret., Eocene; Europe. 



Shell obliquely ovate, with attenuated obtuse beaks, inequi- 

 valve ; one (right ?) valve convex ; the other (left ?) smaller, flat 

 or concave, with a small transverse ligamental groove at the 

 apex ; in the convex valve there is on\y 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 

 Avhich 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. 



Di.Htr. — 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. 



