80 PLIOCENE MOLLUSCA. 



Prof, Sliimer attributes the phenomenon in question to changes in the conditions 

 under which the molhisca may have lived, as, for example, in the temperature or 

 salinity of the water. In the present case the dwarfed and full-sized forms are 

 found in the same deposit, although the former are the most common, possibly 

 indicating, if the view quoted is correct, the existence of an estuarine habitat at no 

 great distance from this part of the Red Crag sea. Dr. 0yen informs me that 

 similar cases of dwarfed mollusca occur in Norwegian waters. 



The comparative abundance of this variety at Oakley suggests that it might 

 also be found at other horizons of the Red Crag, having been mistaken for young 

 specimens of N. granulata or N. pro-pinqua. 



Nassa DoUfusii, sp. nov. Plate V, fig. 9. 



1879. Nassa angulata (f), S. V. Wood (non Brocclii), Moii. Crag Moll., 2n(l Suppl., p, 4, tab. iv, 

 fig. 14. 



Specific Cltar<ictp)'><. — Shell ovate, short, small, thick and strong, with 5 whorls, 

 more or less convex and usually with a deep suture, having 12 to 15 well-marked, 

 elevated and slightly curved longitudinal ribs on the body- whorl, intersected by 

 about 10 strong spiral costse Avhich form a slight tubercular decussation where they 

 cross the ribs, but not of so pronounced a character as in N. granulata or N. pro- 

 jjinqtia ; mouth suborbicular, notched and angular above, less than half the total 

 length ; canal distinct but narrow and very short, inclining to the left ; outer 

 lip thickened outside by a labial rib, having a row of coarse tubercles within, 

 continuous with a series of strongly marked flutings on the inner lip, which is 

 thick and folded back on the columella. The basal part is separated from the rest 

 of the body- whorl by a deep groove, as in N. incrassata. 



Dimensions. — Ii. 10—12 mm. B. G — 8 mm. 



Distridntion. — Not known living. 



Fossil : Coralline Crag : Boyton. Waltonian : Little Oakley, 

 Butleyan : Butley. Probably elsewhere in the Red Crag. 



Remarks. — I have about 20 specimens of a small, strong, and coarsely sculptured 

 Nassa from Oakley, which on the whole seem to correspond with the one figured 

 by S. V. Wood as N. angulata, Broc. Submitting some of them to M. Dollfus he 

 expressed a decided opinion that neither they nor that given by Wood can be 

 referred to Brocchi's species, a view with which, from a comparison of them with 

 some fossils from Altavilla, near Palermo, kindly sent me by the Marchese di 

 Monterosato, I am compelled to agree. 



M. Dollfus equally insists that the Oakley specimens are not a variety of 

 N. incrassata, a form to which they bear some resemblance, and suggests that 

 I should give them a fresh specific name. I venture therefore to dedicate this 



