MAZATLAN UNIVALVES 237 



enriched by 12 from Panama, (of which one, V. minuta, is a 

 Teinostoma, as is also the PNeritina pusiUa from Jamaica of 

 the same author,) consists of a group of exceedingly minute 

 turbinate or discoiclal shells, differing greatly in shape, but 

 agreeing in colour and texture, which are white and subhyaliue. 

 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 Moll., pi. 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 B-otellse by D'Orbigny and 

 others (e. g. Globulus striatus, semi-striatus, pusillus, carinatus 

 and anomalus) are perhaps several Vitrinella). 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 ; t fourteen appear now for the first 



* Dr. Gray proposes to alter the name of this latter genus to Vitrinula. 

 t 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 



with Ethalia or Teinostoma, and do not display the characteristic difference 

 between the earlier and later whirls. 



