MANUAL OF THE MOLLUSCA. 
cones placed one within the 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, 1867. 
Type, P. Bohemica. Upper Silurian. Bohemia. 
Shell like that of Pterotheca, but chambered. 
CLASS CONCHIFERA.* 
[FAMILY ANOMIADZ. | 
The genera included are: ANOMIA (Limanomia) (p. 408), 
PLACUNOMIA (p. 409), PLACUNA (p. 409), CAROLIA (p. 410), 
PLACUNOPSIS (p. 410), and PLACENTA (p. 410). 
FAamMILy J.—OSTREIDE.T 
The genera enumerated are OSTREA (Gryphea, Hxogyra) and 
PERNOSTR@A, 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- 
yalve; test foliaceous, subnacreous, resembling that of Ostrea, 
ng fibrous cortical layers; umbones obsolete; hinge line di- 
verging more or less broad, with 4 to 8 vertical ligamenta’ 
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 serye 
to link the families Ostreide and Aviculide. 
Distribution, 7 species. Middle Lias—, Forest Marble. 
France, England. 
[FAMILY PEOTINIDZ. ] 
Lhe genera are PEcTEN (WNeithea, Pallium), HEMIPEOTEN 
(p. 412), HinwiTEs (p. 412), Lima (p. 412), SpPonDYLUS (p. 413), 
PEDUM (p. 414), PLIcATULA (p. 414), and the following addi- 
tional genera and sub-genera :— 
* See p. 393. + See p. 407, 
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