MAZATLAN UNIVALVES 237 
enriched by 12 from Panama, (of which one, V. minuta, is a 
Teinostoma, as is also the P Neritina pusilla from Jamaica of 
the same author,) consists of a group of exceedingly minute 
turbinate or discoidal shells, differing greatly in shape, but 
agreeing in colour and texture, which are white and subhyaline. 
They have but few, rapidly enlarging whirls: the aperture is 
generally much dilated and sinuated ; the umbilicus is almost 
always large. They are either smooth and glossy; or variously 
ribbed, keeled or striated. In some respects they resemble 
Cyclostrema, in others Adeorbis. - Indeed many of the species 
could not be separated generically from the forms figured by 
the author of the latter genus, Searles Wood, Crag Moil., pl. 15, 
_ except by the texture. All the species examined agree in a 
remarkable disproportion between the nuclear and the adult 
parts of the shell. While the usual number of whirls is four 
and a half, three of these are occupied with the unformed shell, 
which is smooth in the sculptured species, and distinctly mark- 
ed even in the glossy ones ; while only one, or one and a half, 
(very rarely two,) suffice for the full grown portion. From this 
circumstance it might have been supposed that they are all 
young shells: but as they do not in the least resemble the 
young of any larger Mazatlan species, and as more than 150 
individuals were found, all keeping to the same type, it is 
presumed that it indicates a peculiarity in the animal, which 
may serve to distinguish it from neighbouring genera. It is 
exceedingly to be regretted that Dr. Gray should have used 
the name over again last year for a genus of land shells.* 
Among the species described as Rotelle by D’Orbigny and 
others (e. g. Globulus striatus, semi-striatus, pusillus, carinatus 
and anomalus) are perhaps several Vitrinelle. Similar forms 
are also known from the Eastern Seas. It is probable that 
the existing species are extremely numerous, though the indivi- 
duals are few. Although many of the Mazatlan specimens 
were perfectly fresh from their native haunts, not a trace of 
operculum was found. Of the described species, four are 
shewn by the types in Mr. Cuming’s collection to be common 
to Panama and Mazatlan ;+ fourteen appear now for the first 
* Dr. Gray proposes to alter the name of this latter genus to Vitrinula. 
+ Besides these may be seen in the Cumingian collection types of V. valva- 
toides and Teinostoma minutum from Panama; and V., tincta, V. interrupta and 
Ethalia megastoma from Jamaica. The latter, along with a young Natica ? can- 
rena, were found with the specimen of V.interrupta. The indented species, 
ranked with this genus by its author on account of their texture, accord better 
with Ethalia or Teinostoma, and do not display the characteristic difference 
between the earlier and later whirls, 
