28 INFERIOR OOLITE AMMONITES. 



The peculiarities of this species are an inflation and gibbosity of the outer portion 

 and ventral area of the whorl immediately preceding, and up to, the mouth-border ; 

 the very early age at which it becomes quite smooth, merely exhibiting very fine 

 lines of growth (the small ribs shown on fig. 1 are rather too distinct, and are not 

 exhibited by other specimens) ; and the depressed inner portion of the shell extending 

 from the middle of the whorl to the same part of the same whorl opposite. The species 

 from which it is most difficult to separate this are Lioceras opalinum (the open form, 

 Plate XIII, fig. 7), Lioc. decipiens, and Lioc. bradfordense . The fine striae on the 

 type-specimen are produced on the lateral area much more than on the ventral, over 

 which they pass almost at right angles to the keel, and this is especially noticeable 

 on the body-chamber. In fig. 4 the striae are rather more produced on the ventral 

 area, as is shown by the drawing of the mouth -border, but they are quite as much 

 produced on the lateral area. This flexure of the striae enables us to separate the 

 species from Lioc. opalinum, in which the forward sweep of the striae on the ventral 

 area is rather peculiar. Besides this, the greater thickness, the depressed inner 

 portion I have mentioned, the possession of ribs in youth, and the expansion in 

 the umbilicus when the body-chamber is present, separate this species from Lioc. 

 opalinum. From Lioc. bradfordense the separation is not so obvious. The more 

 discoidal form, caused by its being thinner and also by the depressed inner portion ; 

 the fact of its being smooth at a very early age ; the more rounded ventral area of 

 the body-chamber ; the small but suddenly expanding umbilicus (not regular 

 as in Lioc. bradfordense) ; but more especially the very different front view ; these 

 are the chief points of difference. This front view as well as the thinner, less 

 conspicuous carina, the more sloping ventral area, and the larger umbilicus, distin- 

 guish it from Lioc. decipiens. 



Lioc. ambiguum occurs in the Paving-bed (Murchisonce-zone) of Bradford Abbas, 

 and also in a quarry near Sherborne, Dorset ; but is certainly a scarce form. 1 This 

 species has been quoted from Bradford Abbas under the name Am. aalensis, 

 Zieten (Am. candidus, d'Orb), a species which has different sutures, different ribs, 

 different umbilicus, ventral area, and sectional view. 



Plate VII, fig. 1, exhibits a very finely-preserved specimen collected by my 

 father many years ago. Fig. 2 gives the front view, a most characteristic feature 

 in this species. Figs. .3, 4 are the termination of another specimen. Figs. 5, 6, 

 represent a young specimen of this species, fig. 5 marking the open umbilicus 

 caused by the presence of the body-chamber. All the specimens are from 

 Bradford Abbas. 



1 A poorly preserved specimen, doubtfully referred to this species, I obtained from Haresfield 

 Hill, Bed 10, Section V (p. 43). 



