MANUAIi OF THE MOLLUSCA. 



cones placed one within tlie other ; the transverse section of the 

 tubes is circular or subtriangular ; the surface is transversely 

 or longitudinally striated. 



Fossil, 3 species. Lower Silurian. Canada. 



Phragmotheca, Barrande, 186Y. 



Type, P. Bohemica. Upper Silurian. Bohemia. 

 Shell like that of Pterotheca, but chambered. 



CLASS CONCHIPEEA.* 



[Pamily AlSrOMIAD^.] 



The genera included are : Ajj^omia (Limanomia) (p. 408), 

 pLACUNOMiA (p. 409), Plagtjfa (p. 409), Carolia (p. 410), 

 PiiACUNOPSis (p. 410), and Placenta (p. 410). 



PaMLLY I. OSTEEID^.t 



The genera enumerated are Ostrea [Gryphcea, Exogyra) and 



Pernostrcea, Munier-Chalmas, 1864. 



Derivation from Perna and Ostrea. 



Example, Ostrea Luciensis, D'Orbigny. 



Shell more or less thick, adherent by the left valve, sub- 

 circular, squarish, or trapezoidal, nearly equilateral, inequi- 

 valve ; test foliaceous, subnacreous, resembling that of Ostrea, 

 no fibrous cortical layers; umbones obsolete; hinge line di- 

 verging more or less broad, with 4 to 8 vertical ligamental 

 furrows, some long and deep, others short and rudimentary. 

 Muscular impression subcircular or semilunar, deeper in the 

 fixed valve than in the other. 



The species of this genus, with the exception of the liga- 

 mental pits, have nearly all the characters of Ostrea ; they serve 

 to link the families Ostreidce and Aviculidce. 



Distribution, 7 species. Middle Lias — , Porest Marble. 

 France, England. 



[Pamily Pectinid^.] 



The genera are Pecten" {Neithea, Pallium), Hemipecten 

 (p. 412), Hinnites (p. 412), Lima (p. 412), Spondylus (p. 413), 

 Pedum (p. 414), Plicatula (p. 414), and the following addi- 

 tional genera and sub-genera : — 



* See p. 393. t See p. 407. 



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