CONCHIFERA. 321 



ftirnished with a free ossicle ; muscular impressions faint, the anterior elon- 

 gated ; pallial line usually sinuated. ^ 



Animal with mantle margins united ; siphons long, more or less united, 

 fringed ; gills single on each side, the outer lamina prolonged dorsally beyond 

 the line of attachment. 



Plwladomya and its fossil allies have an external ligament only ; Coch^ 

 lodesma and Pandora have no ossicle. The external surface of these shells 

 is often rough with large calcarious cells, sometimes ranged in lines, and 

 covered by the epidermis ; the outer layer consists of polygonal cells, more 

 or less shai-ply defined ; the inner layer is nacreous. 



Anatina, Lamarck. Lantern-shell. 



Ti/pe, A. rostrata, PI. XXIII. fig. 7. {Anatmus, pertaining to a duck.) 



Sijn. Laternula, Bolten M. S. Auriscalpium, Muhlf. Osteodesma, Bl. 

 Cyathodonta (undulata) Conrad ? W. America. 



Shell oblong, ventricose, sub -equi valve, thin and translucent, posterior 

 side attenuated and gaping ; umbones fissured, directed backwards, supported 

 internally by an oblique plate ; hinge with a spoon-shaped cartilage-process 

 in each valve, fui-nished in front with a transverse ossicle ; pallial sinus wide 

 and shallow. 



Animal with a closed mantle and long united siphons, clothed with 

 wrinkled epidermis; gills one on each side, thick, deeply plaited; palpi very 

 long and narrow ; pedal opening minute, foot very small, compressed. 



Distr. 20 sp. India, Philippines, New Zealand, W. America. 



Fossil, 50 sp. Devonian ? — Oolite — . U. States, Europe. 



Suh-genera. Periplo7va (inequivalvis) Schum. " Spoon-hinge" of Petiver ; 

 oval, inequivalve, left valve deepest ; posterior side very short and contracted. 

 Distr. "VV. Indies, S. America. 



Chchlodesma, Couthony, C. prsetenue, PI. XXIII. fig. 8. (Bontia, 

 Leach MS. Ligula, Mont, part.) Oblong, compressed, thin, slightly inequi- 

 valve ; umbones fissured ; cartilage processes prominent, without an ossicle ; 

 pallial sinus deep. Animal with a broad, compressed foot ; siphons long, 

 slender, divided throughout ; gills one on each side, deeply plaited, divided by 

 an oblique furrow into two parts, the dorsal portion being nai'row'er, com- 

 posed of a single lamina only, and attached by its whole inner surface. {Han- 

 cock) Distr. 2 sp. U. States, Bxit. Medit. Fossil, Pliocene, Sicily. 



Cerconnja, Agassiz. C. undulata, Sby. (= Rhynchomya, Ag.) Shell 

 very thin, elongated, compressed, attenuated posteriorly ; sides concentrically 

 fiuTowed, umbones fissured, posterior (cardinal) area more or less defined. 

 Fossil, 12 sp. Oolite — Neocomian; Europe. 



Thracia (Leach) Bl. 

 St/n. Odoncinetus, Costa. Corimya, Ag. Rupicola (concentrica) Bellevue. 



