MAZATLAN UNIVALVES 187 
somewhat of an approach to it, itis presumed (in the absence 
of knowledge of the animal) to be an aberrant variety. 
Hab.—Mazatlan ; extremely rare ; L’pool 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 or dinary indentation i in the labrum. 
243. IANTHINA DECOLLATA, 20”. prov. 
I. t. glohosd; spird plus minusve extante, pallide violaced ; 
anfractu ultimo pallidissimo, basim versus violaced ; apice 
corneo, deciduo : nucleo obliquo, haud extante ; suturd profunda ; 
labro varie sinuato; columella via contorté ; labio haud por- 
recto, umbilicum sepe tegenie. 
Comp. Ianthina globosa, Swains. Zool. Til. vol. i. pl. 85, fig. med. 
Comp. Ianthina prolongata, D’Orb., B. M. Cat. Cuba Moil. 
p. 23, no. 259; B. WM. Cat. D’ Orb. Moil. p. 35, no. 317; non 
Desh. in iBone: An. s. Vert. vol. 1x. 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 European species resembles that of 
Lymnea (Desh.) 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, ,, ASA SLs 130°. 
Hab.—Mazatlan ; with I. striulata, extremely rare ; L’pool Col. 
Tablet 878 contains 3 specimens. 
