450 CEETACEOTJS PELECTPODA 



changes vary greatly with the state of preservation of the surface. A closely allied 

 ^ViVoj)Q2in ^^Qoiesi^ Spondylus globulosus, d'Orb., only differing from the Indian 

 form by a little more distant radiating ribs and comparatively larger ears. 



Localities, — East of Parally, Moraviatoor, Odium, in yellowish compact or 

 sandy limestone, 



Formation, — Ootatoor group. 



XLIV. Family— FLA QVNIBJE. 



The animal of the typical species, Flacuna placenta^^ Linne, is symmetrical; 

 it has the mantle margins perfectly separated, surrounded with smaller and larger 

 cirri, and internally furnished with a kind of a pendent border, as in most species 

 of the F^cTiNiBM : one pair of sub-equal gills on each side, long, crescent-shaped, 

 posteriorly attenuating to a point and united ; adductor muscle moderate, sub-cen- 

 tral, round, single ; at the posterior side of it is a small, indistinct impression caused 

 by the branchiopallial muscle, and near the hinge a third, also small, but more dis- 

 tinct, impression of the pedal muscle ; foot sub-cylindrical, tubular, and expansible ; 

 lips large, sub-triangular ; ventricle of the heart free ; generative organ and rectum 

 attached to the right mantle-lobe. 



Shell equivalve, or very nearly so, compressed, thin, of a pearly tubular 

 structure, externally becoming often finely lamellar ; ligament marginal, cartila^'e 

 attached to the external side of two diverging ribs in one valve, correspondino' 

 to two similar grooves or ribs in the other valve ; muscular scar sub-central, round. 



Gray more than 20 years ago suggested the separation of Flacuna and its 

 allies into a distinct family ; but since the examination of the animal of Fl. placenta 

 by Woodward, it has been thought better not to separate them from the Anomiidm. 

 The organization of both is no doubt very similar, but we find that one of the 

 most important characters of the Anomiid^, the peculiar development of the byssal 

 muscles, is altogether wanting in the Flacunibm; the shells of this last family 

 are, besides, symmetrical, equivalve, or sub-equivalve, free, supplied with a marginal 

 ligament and internal cartilage. The habitat is also very different. Flacuna is 

 found on sandy shores, and has a very extensible vermiform foot, with which it can 

 bury itself partially in the sand, spinning at the same time a few threads of byssus. 

 Flacunertia I found loosely lying on coral-reefs. The third genus referred to this 

 family is based upon a peculiar fossil shell from the eocene of Paris, for which 

 Deshayes suggested the name Semiplicatula. Of this last genus, an aberrant 

 form occurs in the South Indian cretaceous deposits; it will be noticed subse- 

 quently. Of the former genera, a few fossil species have been noticed from tertiary 

 deposits only, but none from older formations. For one or two noted from creta- 

 ceous rocks a new generic name has been proposed by Conrad, and the Jurassic 

 species have been named Flacunopsis ; both are referable to the Anomiid^. 



^ See Woodward in Ann. and Mag. Nat. Hist., 2nd ser., xvi, p. 25. 



