268 MANUAL OF THE MOLLUSCA. 



230 fms. (A. imbricata, Poll). Prince- Regent Inlet (A. glacialis] A. sca- 

 phula, Benson, is found in the Ganges and its branches, from Calcutta to 

 Humeerpoor on the Jumna, 1000 miles from the sea. 



Fossil, 200 sp. L. Silurian . U. S. Europe; S. India. 



CUCULLJSA, Lamarck. 



Etym. Cucullus, a cowl. Type, C. concamerata, PI. XVII. fig. 14. 



Shell sub-quadrate, ventricose; valves close, striated; hinge-teeth few 

 and oblique, parallel with the hinge-line at each end ; posterior muscular 

 impression bounded by an elevated ridge. 



Distr. 1 sp. Mauritius, Nicobar, China. 



Fossil, 100 sp. L. Silurian . N. America, Patagonia, Europe. 



Sub-genus, Macrodon, Lycett. M. Hirsonensis, PI. XVII. fig. 15. Shell 

 with a few oblique anterior teeth and one or more long laminar posterior 

 teeth. The Ark-shells of the Palaeozoic and secondary strata have their 

 anterior teeth more or less oblique, like Area, the posterior teeth parallel 

 with the hinge-line like Citculfaa ; their valves are close or gaping below ; 

 their umbones frequently sub-spiral ; and the hinge-area is often very narrow, 

 and in some species only the posterior moiety is visible. 



PECTUNCULUS, Lam. 



Type, P. pectiniformis, PL XVII. fig. 16. (Area pectunculus, L.) 



Shell orbicular, nearly equilateral, smooth or radiately striated ; umbones 

 central, divided by a striated ligamental area; hinge with a semicircular 

 row of transverse teeth ; adductors sub-equal ; pallial line simple ; margins 

 crenated inside. 



Animal with a large crescent- shaped foot, margins of the sole undulated ; 

 mantle open, margins simple, with minute ocelli ; gills equal, lips continuous 

 with the gills. 



Distr. 50 sp. W. Indies, Brit. India, N. Zealand, W. America: ranging 

 from 8 to 60, rarely 120 fathoms. 



Fossil, 70 sp. Neocomian . U. S. Europe: S. India. 



The teeth of Pectunculus and Area increase in number with age^ by 

 additions to each end of the hinge-line, but sometimes the central teeth are 

 obliterated by encroachments of the ligament. 



LIMOPSIS, Sassi, 1827. 



Type, L. aurita, PL XVII. fig. 17. Syn. Trigonocoelia, Nyst. 



Shell orbicular, convex, slightly oblique ; ligamental area with a triangular 

 cartilage-pit in the centre ; hinge with 2 equal, curved series of transverse 

 teeth. 



Distr. 1 sp. Red Sea (Nyst.) 



Fossil, 17 sp. Bath-oolite . U. States; Europe. 



