384 MOLLUSC A SUB-KINGDOM vi 



Superfamily 8. ANOMIACEA. Herrmannsen. 



Shell monomyarian, not alate ; edentulous or Isodont, usually sessile ; shell substance 

 nacreous, tubuliferous, with traces of a prismatic layer; area obscure, usually small, 

 amphidetic ; ligament obscure, with an alivincular internal resilium ; gills filibranchiate, 

 mantle lobes free ; foot small, grooved, digitiform ; dioecious ; marine. 



Family 37. Anomiidae. Gray. 



Shell variable, irregular and inequivalve when sessile, byssiferous when young; in 

 most genera the byssus becomes modified to a calcified or horny plug passing through a 

 foramen in the attached valve, and fastened to other objects, a condition which may be 

 permanent or transient ; area small, amphidetic ; ligament amphidetic, more or less 

 internal, supplemented by an internal resilium, for which the crura serve as chondrophores, 

 ali- or multivincular ; hinge usually edentulous, rarely rugose, with amorphous inter- 

 locking rugosities ; posterior adductor small, sub-central, in the sessile forms reinforced by 

 the pedo-byssal muscles, which are modified for service as adductors. ? Devonian. Jura 

 to Recent. 



Anomia, Mull. Shell thin, sessile by the calcified byssus passing through a sinus 

 or perforation in the right valve, conforming to the subjacent surface ; the left valve 



more convex, with four muscular scars on 

 a central area ; a chondrophore in the 

 lower valve. Jura to Recent. 



? Limanomia, Bouch. Devonian. 

 Hypotrema, d'Orb. Jura and Cretaceous. 

 Placunanomia, Brod. Miocene to Recent. 

 Carolia, Cant. (Fig. 676). Shell 

 orbicular, compressed, radially striated ; 

 right valve with a byssal foramen nearly 

 closed in the adult ; resilium much as in 

 Anomia ; adductor scar single. Eocene ; 

 Egypt. 



Sub-genus : Wakullina, Dall. Smooth ; 

 byssal foramen obsolete ; the resilium received 

 on diverging crura in the upper valve. Oligo- 

 cene ; Florida. 



Placenta, Retzius (Placuna, Brug.; 

 Placunema, Stol. ; Pseudoplacuna, Mayer). 

 Shell free, orbicular, thin, very compressed ; 

 the resilium with long, unequal crura. 

 Tertiary and Recent, 



Ephippium, Bolten. Like Placenta, 

 but the shell radially waved ; young with a small byssal perforation, which becomes 

 closed and obsolete in the adult. Tertiary and Recent. 



Placunopsis, Morr. and Lye. Shell rounded, imperforate, free, or sessile. Jura, 

 Hemiplicatula, Desh. (Semiplicatula, Fisch.) ; Saintia, Rainc. Eocene. Paranomia, 

 Conrad. Ripley Group. Monia, Gray. Miocene ; California. 



i 

 V. DYSODONTA. Neumayr (emend.) 



Superfamily 9. MYTILACEA. Ferussac. 



Shell anisomyarian, usually equivalve, not alate or notched for a byssus, edentulous 

 or Dysodont ; shell substance sub-nacreous, rarely more or less prismatic, with a conspicu- 



FIG. (576. 



Carolia placunoides, Cantr. Eocene; Wadi el Tih, 

 near Cairo, Egypt. Interior of both valves, 2/ 3 . 



