286 varix. 



UPPER- VALVE. The free valve in attached bivalves. 



UVIGERINA. D'Orb. A genus of microscopic Foraminifera. 



VAGINA. Megerle. Solen vagina, Auct. 



VAGINULA. (A little sheath, the husk of corn.) Class, Ptero- 

 poda, Lam. — Descr. Pyramidal, slightly inflated in the centre, 

 thin, fragile ; aperture oblong, with the edges turned slightly 

 outwards. — Obs. The little shells of this genus, which are only 

 known in a fossil state, differ from Cuvieria in being pointed at 

 the extremity. Found in the tertiary beds of Bordeaux. V. Dau- 

 dinii, fig. 225. 



VAGINULINA. D'Orb. A genus of microscopic Foraminifera. 



VALVATA. Mull. Fam. Peristomata, Lam. Cricostomata, Bl.— 

 Descr. Thin, turbinated ; spire short, composed of from three to 

 six rounded whorls ; aperture circular ; peritreme acute, entire ; 

 operculum horny, spiral. — Obs. This genus of small shells resem- 

 bles Cyclostoma, from which the recent species may be known 

 by the horny texture of the external surface, being fresh-water 

 shells. The fossils of course belong to the fresh-water formations. 

 V. piscinalis, fig. 322. Europe and North America. 



VALVES. (Valva, a door, a folding piece.) The two pieces 

 composing a bivalve shell, which close upon each other, turning 

 upon a hinge consisting of a ligament, cartilage, and teeth. 

 See Bivalve, Multivalve, and Univalve. 



VALVULINA. D'Orb. A genus of microscopic Foraminifera. 



VARIX. {A swelling vein.) A varix is formed on the outer surface 

 of a spiral shell, by the thickened, reflected edge of a former 

 aperture, after fresh deposits of testaceous matter have increased 

 the size by adding to the growth of the shell beyond it. In this 

 manner there are frequently many varices, or edges of former 

 apertures, in various parts of the spire and the body whorl. They 

 are sometimes placed at regular distances from each other, as in 

 Harpa, fig. 419 ; sometimes continuous, as in Ranella, fig. 394 ; 

 sometimes discontinuous, as in Triton, fig. 398 ; sometimes ramose, 

 as in Murex, fig. 395 ; sometimes simple, as in Scalaria, fig. 351 ; 

 sometimes spinose, as in Murex spinosus. The term varix has 



