MAZATLAN UNIVALVES 187 



somewhat of an approach to it, it is presumed (in the absence 

 of knowledge of the animal) to be an aberrant variety. 

 Hob. Mazatlan ; extremely rare ; ISpool Col. 



Tablet 877 contains the extreme specimen, and a younger 

 one, intermediate. The larger sp. is but slightly waved in the 

 outer lip : another, however, with the same twisted columella, 

 presented the ordinary indentation in the labrum. 



243. IANTHINA DECOLLATA, nom.prov. 



I. t. globosa ; spird plus minusve extante, pallide violaced ; 

 anfractu ultimo pallidissimo, basim versus violaced ; apice 

 corneo, deciduo ; nucleo obliquo, haud extante ; suturd profundd ; 

 labro varie sinuato ; columella vix contortd ; labio haud por- 

 recto, umbilicum scepe tegente. 



Comp. lanthina globosa, Swains. Zool.ILl. vol. ii. pi. 85, fig. med. 

 Comp, lanthina prolongata, DOrb., B. M. Cat. Cuba Moll. 



p. 23, no, 259 ; B. M. Cat. D'Orb. Moll. p. 35, no. 317 ; non 



Desk, in Lam. An. s. Vert. vol. ix. p. 5, no. 3. 



This shell is most closely related to the West Indian species, 

 differing from the specimens examined simply in colour, which 

 instead of being equally diffused on the shell, is confined to 

 the .base and spire. It differs from I. prolongata of the Medi- 

 terranean and Canaries in the very slight contortion of the 

 columella, which in the Europsean species resembles that of 

 Lymnsea (Desk.) If the I. globosa of Swains, represents the 

 W. Indian shell, and not the I. prolongata, as Desh. and Gray 

 suppose, this shell may prove identical with it, when more 

 specimens have been found from other localities. The Mazat- 

 lan specimens, though very few, differ considerably in the 

 greater or less exsertion of the spire, inflation of the shoulder 

 and base of the body whirl, and concealment of the umbilicus. 

 The sinuation of the outer lip varies not only in different speci- 

 mens, but in the same shell at different periods ; being some- 

 times scarcely waved, at others strongly angulated as in I. fragi- 

 lis, sometimes with a semicircular medial sinus. The nucleus 

 is sunken, rather oblique, with the apex horny and always de- 

 collated. In I. prolongata, it is exserted and persistent. The 

 largest sp. measures long. 1'02, long, spir. "3, lat. "87, div. 105. 

 A swollen sp. measures *83, *13, *81, 130. 



Sab. Mazatlan ; with I. striulata, extremely rare ; L'pool Col. 



Tablet 878 contains 3 specimens. 



