* 
F. B. Meek on the Family Pteriide. 215. 
The animal in the existing typical genus has the mantle-mar- _ 
ns freely open and doubly fringed; foot small, grooved, and 
aving the power of spinning a byssus; palpi large; gills two 
on each side, crescent shaped, free or connected with each other 
posteriorly, and to the mantle. 
The foregoing diagnosis of the shells of this family is framed 
80 as to include species belonging to three subordinate groups, 
the first of which, so far as known to the writer, has no living 
representatives, and seems to have been mainly confined to the 
Paleozoic epoch. The other two groups (the Pieriine or Avicu- 
line and Melinine) are both represented by living species in 
our existing seas. These three sections or subfamilies may be 
characterized as follows :— 
1. Prerinny.x, (or Pterinia group). : 
Cartilage apparently occupying a series of linear furrows, ranging more 
or less nearly parallel to the cardinal margin, in a usually broad, flat- 
tened cardinal facet or area, Anterior muscular scar sometimes mode- 
horhynchus, and several undefined Paleozoic groups. A part of the 
2. Prerunx, (or Aviculine). 
Cartilage mainly or entirely confined to a single, more or less defined, 
depression or cavity behind the beaks. Anterior muscular impression 
very small, . 
Includes Pteroperna, Pteria (or Avicula), Margaritifera, Malleus, 
Aucella and Eumicrotis. The following extinct genera also probably 
belong here, viz:—Monotis, Halobia, Pteronites and Posidonomya, with 
apparently some undescribed fossil genera. 
3. Meuninz, (Perna or Isognomon group.) , 
Cartilage divided and distributed along the hinge in a series of furrows 
crossing the cardinal area at right angles to the hinge line. Anterior 
muscular scar generally very small. - : 
neludes Crenatula, Melina (= Perna Brug., not Adanson), Bakevellia, 
lia, Inoceramus and Pulvinites. 
and interior of a greater number of fossil species are known. 
i ] as hinge 
© Megambonia aviculoides, and M. lamellosa Hall, for instance. 
