474 MOLLUSCA. 
irregular and more isolated streaks of the last whorls (see fig. 5); sometimes two of 
the streaks are placed close together and each separated by wider interstices from the 
others (see fig. 3). 
The true NW. striolata, Lister, Hist. Conch. t. 604. fig. 29; Récluz, Rev. Zool. 184], 
p. 337; Sow. Thes. Conch. figg. 98, 99; Reeve, fig. 100, from Venezuela and Guiana, 
seems to be an analogous variation of WV. zebra, Lam., characterized by a similar 
deficiency and irregularity of the streaks; but it is of a generally broader shape than 
the Central-American forms, the spire is shorter and flatter, and the last whorl shows 
a very slight subangulated swelling below its greatest circumference. 
5. Neritina cassiculum, (Tab. XXVIII. figg. 9, 9 a.) 
Neritina cassiculum, Sowerby, Conch. Illustr. sp. no. 55, fig. 55 (1837) *; Thes. Conch. ii. p. 521, 
t. 11]. fig. 1927; Menke, Zeitschr. f. Malak. 1851, p. 166°; Reeve, Conch. Icon. ix., 
Neritina, t. 26. fig. 118‘; P. Carpenter, Cat. Mazatlan Shells, p. 258°; Binney, Land and 
Freshw. Shells of N. Am. iii. p. 105, fig. 210 (copied from Sowerby) *; Fisch. & Crosse, 
Miss. Scient. Mex., Moll. ii. p. 484, t. 58. figg. 8, 8a, 5”. 
Peculiarly globose, rather swollen in the upper part of the last whorl; spire a little prominent, but nearly flat 
at the top, very obtusely subangulated in the lower half of the last whorl. Yellowish-green, with very 
numerous white spots, which have a black point towards the aperture. Columellar plane a little swollen, 
white, orange at its outer border. Columellar margin not sinuated in the middle, with numerous (11) 
small obtuse teeth, one of the upper ones at the upper third of the margin twice as broad as the rest. 
Diam. maj. 17, min. 104, alt. 17, marg. col. 103, lat. areee 6-7 millim. 
Hab. N.W. Mexico: Mazatlan (Melchers?; Reigen®"). 
In general appearance and colour this species very much resembles WV. virginea, var. 
listert, Pfr., from Cuba, but differs from it in the flatter top and the slight angulation 
in the lower part of the last whorl. P. Carpenter® suggests that it may be a variety 
of N. picta, but he himself mentions the difference in the form of the teeth of the 
columellar margin. I have not yet seen the operculum of NV. cassiculum, but, to judge 
from the formation of the columellar margin, it is probably like that of the subgenus 
Neritea, i. e. with the two apophyses completely separated, whereas in NV. picta they 
are united by a septum, which is the character of the subgenus Clithon. 
When I wrote my monograph of Neritina, in the second edition of Martini and 
Chemnitz’s work, I had not seen a specimen of the present species from Mazatlan, 
and so I identified it with the reticulated variety of V. reclivata. ‘Two examples from 
Mazatlan, from Dunker’s collection, are, however, now before me, and from these the 
above description has been taken. Nevertheless, it is not quite certain whether the 
original WV. cassiculum of Sowerby, the habitat of which is unknown, is really the 
Mazatlan species or the variety reticulata of N. reclivata. 
6. Neritina virginea, var. listeri. 
Nerita maculis ad interstitia latis and N. major, Lister, Hist. Conch. t. 604. figg. 26, 380 (1688)’. 
Nerita virginea (Lam.), Chemnitz, Syst. Conch.-Cab. (ed. 1) ix. p. 72, t. 124. fig. 1086 *. 
