252 G. C. Crick — Note on Ammonites euomphalus, Sharpe. 



one side witli those on the opposite side are thicker than the rest, 

 the posterior one of each pair being the thicker of the two ; this is 

 especially the case where the diameter of the shell is 10 mm. At 

 the middle of the periphery each rib bears a very feeble tubercle : 

 on each side of this and about half-way between it and the large 

 lateral spine, there is another rather more prominent, but still feeble, 

 tubercle. The tubercles on the thickened ribs, especially on the 

 posterior one of each pair connecting the large spines, are relatively 

 larger than the rest, 



Sharpe gave the dimensions of the type-specimen as follows : — 

 Diameter, three-fourths of an inch ; width of aperture, half an 

 inch ; height of the last whorl, one-third of an inch. My own 

 measurements of this specimen are: — Diameter of shell, 21'5ram. ; 

 ■width of umbilicus (at suture of shell), 8-5 mm. ; height of outer 

 "whorl, 8 mm. ; height of outer whorl above preceding whorl, 

 ^'5 mm. ; thickness of outer whorl, 10"25 mm. 



In 1896 Mr. A. J. Jukes-Browne recorded,^ but did not figure, 

 an example of this species from the " sandy chalk. Bed 13 of 

 Mr. Meyer, in the clifif below Whitlands coastguard station, west of 

 Lyme Eegis." This specimen belongs to the Survey collection at 

 Jermyn Street Museum, and is represented in the accompanying 

 figures (Figs. la-c). It is completely septate, and has a diameter 



$t1^ 



Fig. 1. — DouviUeiceras euomphahts (Sharpe). — a, lateral view; b, peripheral view 

 of the same specimen; c, suture-line of the same example as seen at the 

 place marked s in a and b. From " sandy chalk, Bed 13 of Mr. Meyer, in 

 the cliil below Whitlands coastguard station, west of Lyme Regis." Drawn 

 of the natural size from an example in the Museum of Practical Geology. 



of 40*5 mm., being therefore much larger than Sharpe's type- 

 specimen. Owing to the imperfection of the anterior part of the 

 fossil its dimensions can be best taken at a diameter of 38 mm. 

 These are : — Diameter of shell, 38 mm. ; width of umbilicus (at 

 suture of shell), 15 mm.; height of outer whorl, 14-5 mm. ; height 



1 Quart. Journ. Geol. Soc, vol. Hi (1896), p. 165. 



