252 G. C. Crick — On Ainmonites Ramsayanus. 



belonging to the Bath Museum that I think is referable to Sharpe's 

 * species.' The specimen is labelled " Chalk marl : Evershot." The 

 dimensions of the type-specimen as given by Sharpe are : — Diameter, 

 1\ inch [or about 38 mm.] ; height of the last whorl, f inch [or 

 about 16 mm.] ; width of the aperture, ^ inch [or about 12-75 mm.]. 

 On account of the malformation of the specimen the width of the 

 umbilicus is not quite the same on the two sides, but according to 

 Sharpe's figures, which from their other measurements appear to be 

 drawn of the natural size, the width of the umbilicus on the side 

 represented in his fig. 4a is 11 mm. These dimensions expressed 

 in terms of the diameter, when this is taken as 100, are : — Diameter, 

 100 ; height of last whorl, 4:1 -66 ; width of the aperture (or thickness 

 of the last whorl), 33-33 ; width of umbilicus, 30. 



The dimensions of the present specimen, of which rather more 

 than half the outer whorl belonged to the body-chamber, are : — 

 Diameter, 35-5 mm. (100) ; height of the outer whorl, 14 mm. 

 (39 -43) ; thickness of the outer whorl (or width of the aperture), 

 13-5 mm. (38-0); width of umbilicus, 11mm. (32-27). The 

 specimen is well preserved and very nearly sj^mmetrical, each side 

 closely resembling the lateral view depicted by Sharpe in his fig. 4a, 

 and the transverse section of the whorl agreeing very closely with 

 his fig. 4c. 



Compared with Sharpe's type-specimen, however, the present 

 example exhibits some differences. It has a slightly wider umbilicus ; 

 the ribs on the lateral area are more distinct and regular even up to 

 the anterior end of the specimen, but less numerous, being only 

 sixteen in number on the outer whorl, and, in passing from the 

 umbilicus towards the periphery, are more forwardly inclined, whilst 

 the lateral tubercle is nearer the middle of the lateral area. The 

 greatest diiference, however, is in the character of the periphery. 

 The whole of the periphery of Sharpe's type-specimen is broadly 

 rounded from side to side. This is not quite the case in the present 

 specimen. The periphery of the earliest portion of the outer whorl 

 is on the whole broadly rounded but not regularly convex ; one side 

 is convex, but the other is somewhat flattened and in part depressed, 

 so that the periphery of this portion of the outer whorl bears a feeble 

 groove which is not quite in the median line. At a subsequent 

 stage, i.e. at a short distance from the commencement of the outer 

 whorl, two broad shallow grooves, about 3-5 mm. apart, appear 

 (one a little earlier than the other) one on each side of the median 

 line, and almost close to the margin, of the periphery ; these 

 gradually deepen as the whorl increases in size, and at the anterior 

 end of the specimen are about 5 mm. apart. 



The ribs on the two sides are not opposite but alternate; each 

 bears a rather small compressed transversely-elongated tubercle at 

 the umbilical margin, and a similar but more prominent tubercle 

 at about the middle, or rather outside the middle, of the lateral area. 

 On about the first half of the outer whorl each rib bifurcates, 

 though not very distinctly, at the lateral tubercle, and the broad 

 feeble branches cross the periphery, sometimes a little irregularly, 



