260 THE LAMELLIBRANCHIA 
Odontoperna, Frech ; fossil from the Trias. Inoceramus, Sowerby ; fossil 
from the Jurassic to the Cretaceous. 
Sus-OrDER 4. PECTINACEA. 
Lamellibranchia with an open mantle and devoid of an anterior 
adductor muscle. The gills are folded, and the filaments at the summits 
and bottoms of the folds are different from the others. The gonads are 
contained in the visceral mass and generally open into the kidneys. 
Foot usually rudimentary. 
WSS 
SS 
RS 
R 
aS 
S> 
\ 
\V/ c 
al. Ife 
pea 
Fic. 235. 
Pecten jacobaeus, ventral aspect. a, anus; eé, pallial eyes; f, foot; g, gill; h.a, posterior 
adductor; 7, intestine; /, lips; l.p, labial palps; m, mouth; ov, ovary ; pa, mantle (reflected 
edge) ; p.c, pallial cavity ; sh, shell; ¢, testis. (After Poli.) 
Faminy 1. VULSELLIDAE, Adams. Mantle open ; foot without byssus ; 
the shell high and the hinge without teeth. Genus—Vudlsella, Lamarck. 
Faminy 2. AVICULIDAE, Swainson. Foot provided with a very stout 
byssus (Fig. 236). The gills fused to the mantle ; shell very inequilateral ; 
the cardinal border straight, provided with two auriculae, of which the 
posterior is the longer. Genera—Avicula, Bruguitre ; the auriculae of 
the shell very prominent; heart attached to the ventral face of the 
rectum ; British ; fossil from the Devonian to the present day. 
Meleagrina, Lamarck; shell sub-quadrangular, the auriculae not very 
prominent. A species of this genus, Meleagrina margaritifera, from 
the Indian Ocean, Persian Gulf, etc, forms precious pearls. Malleus, 
Lamarck ; shell irregular, high and narrow, with broad subequal 
The following genera are exclusively fossil :—Limopteria, 
auriculae. 
