ANOMIID^. 293 



Shell suborbicular, very variable, translucent, and slightly 

 pearl}- within, attached by a plug passing through a hole or 

 notch in the right valve ; upper valve convex, smooth, lamellar 

 or striated ; interior with a submarginal cartilage-pit, and four 

 muscular impressions, three subcentral, and one in front of the 

 cartilage ; lower valve concave, with a deep, rounded notch in 

 front of the cartilage-process ; disk with a single (adductor) 

 impression. 



Animal with the mantle open, its margins with a short double 

 fi'inge ; lips membranous, elongated ; palpi fixed, striated on both 

 sides ; gills two on each side, united posteriorly , the outer laminae 

 incomplete and free ; foot small, cylindrical, subsidiary to a 

 lamellar and more or less calcified byssal plug, attached to the 

 upper valve by three muscles ; adductor muscle behind the 

 byssal muscles, small, composed of two elements ; sexes dis- 

 tinct ; ovarj' extending into the substance of the lower mantle- 

 lobe. 



" There is no relationship of affinity between Anomia and 

 Terebratula, but only a resemblance through formal analogy ; 

 the parts which seem identical are not homologous." — Forbes. 



The Anomise are found attached to oysters and other shells, 

 and frequently acquire the form of the surfaces, with which their 

 growing margins are in contact. 



PATRo, Gray, 1849. Shell suborbicular ; two upper scars small, 

 the lower one large. A. ely7'os, Gray (cxxxiiii, 25). 



ENIGMA, Koch, 1845. Shell oblong, transverse. JE. senig- 

 viatica, Chemn. (cxxxi, 76). Lives attached to trees in mangrove- 

 swamps. 



LiMANOMiA {Grayano,)^ Bouchard. Fossil, 4 sp. Devonian; 

 Boulogne. Inequivalve, valves thin near the beaks, slightl}' 

 radially ribbed ; lower valve with a irigonal cut under the ear 

 and near the beak. 



PLACUNOPSis, Morr. and Lj^cett, 1853. Suborbicular, generally 

 somewhat irregular, inequivalve ; larger valve convex, with small 

 submarginal, submedian beak, and mostly ornamented with 

 radiating ribs or striae ; smaller valve flat, free, or attached to 

 foreign objects ; hinge toothless, with a small cartilage-pit in 

 each valve ; muscular scar large, subelliptical, subcentral. Type, 

 P. Jurenais^ Roem. All the species as yet known are from 

 Jurassic deposits, but it is not certain whether all the Jurassic 

 species referred to Placunopsis agree with the characteristics 

 above noticed ; many of them appear to belong to Anomia 

 (t^'pical), and doubts are expressed on this point even regarding 

 the type species, P. Jurensis. 



Placunanomia, Broderip, 1832. 

 Distr. — 13 sp. West Indies, Britain, New Zealand, California, 



