MANUAL OF THE MOLLUSCA. 
smooth, and ornamented posteriorly, as also the free portion 
of the right valve, by concentric plications or radiating ribs. 
Hinge area triangular, transverse, striated in the same 
direction, edentulous, sometimes produced in the middle line; 
lgamental furrow median, longitudinal, straight, rather nar- 
row. Muscular scar near the posterior margin; pallial line 
wanting. Externally the shells of this genus resemble those 
of Hinnites and Ostrea. 
Fossil, 5 species. Lower— Upper Lias. France, Germany, 
Great Britain. 
Paminy I].—AvicuLipZ.* 
Sub-family 1.—PTERINEINz. Cartilage contained in a 
series of linear furrows nearly parallel to the cardinal margin ; 
hinge-margin broad, flat; anterior muscular scar moderately 
developed and deep. Extinct. 
Genus :—PTERINEA (probably includes the Silurian and 
Devonian species referred to Avicula). ae 
Sub-genus :—Zopteria, Billings; HH. Typica, L. Sil. New- 
foundland. Valves equally conyex, hinge with an external (?) 
ligament. 
' Monoprerta, Meck, 1863. 
Type, Gervillia longispina, Cox. Coal Measures. Kentucky. 
Hinge edentulous; anterior muscular scar faint, as in Avicula. 
MYALINA (see p. 421). AMBONYCHIA (p. 417), (?) ACTINO- 
DESMA, and PTEROPERNA (p. 416). A. Casei (Megapteria, Meek), 
Lower Silurian, Indiana, differs from the typical forms of the 
genus in the great development of its posterior wing. 
Sub-family 2.—AvicuLinzZ. Cartilage pit single, defined ; 
anterior muscular scar very small. 
Genera :—AVICULA (Maleagrina, Malleus), VULSELLA (p. 416); 
AUCELLA (p. 416), Monoris (p. 417), HALoBIA (p. 417), Postbo- 
NOMYA (?) CARDIOLA (p. 417); HURYDESMA (p. 417). 
Sub-family 3.—PERNIIDm. Cartilage contained in a series 
of transverse furrows. Anterior muscular scar generally very 
small. 
Genera :—PERNA (p. 418), CRENATULA (p. 418), HYPOTREMA 
(p. 418), GERVILLIA (p. 418), BAKEWELLIA (p. 418), and Iwocz- 
RAMUS (p. 419), and the following additional genera :— 
* See p. 415. 
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