VARIX. 



307 



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



VALYATA. Muller, 1774. Fam. Peristomata, Lam. Cricos- 

 tomata, BL— Deser. Thin, turbinated ; spire short, composed of 

 from three to six rounded whorls ; aperture circular ; peritreme 

 acute, entire ; operculum horny, spiral, — Ohs. This genus of 

 small shells resembles Cyclostoma, from which the recent species 

 may be known by the horny texture of the external surface, 

 being fresh-water shells. Europe and North America. The 

 fossils of course belong to the fresh-water formations. V. pis- 

 cinalis, fig. 322. 



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 Unit al ye. 



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



VANICOEO. Quay and Graimard. A genus of beautiful shells, 

 something like Sigaretus in form, admitted by Mr. Sowerby in 

 the genus Neritopsis, but differing from that genus in the 

 form of the columella. The type is Nerita canceUata, Chemnitz. 

 Mr. Ciiming's collection contains twenty-four species, all of 

 which are cancellated. The operculum is thin, horny, and 

 semicircular, only half enclosing the animal. Ex. V. cidaris. 

 PI. xxvii. fig. 584. 



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 

 Eanella, 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 ia Murex spinosus. 

 The term varix has also been applied to any swelling ridge, such 

 as that on lower part of the columella of AncUlaria, fig. 456. 



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