78 INFERIOR OOLITE AMMONITES. 



so characteristic of Ludwigia, as well as the other often-mentioned differences 

 which exist between the suture-lines of the two genera. 



The other differences between the two species may be well observed on PL XV, 

 where I have placed them together. Lud. rudis possesses coarse ribs, more con- 

 spicuous (especially in the young), on the inner area; they very frequently bifur- 

 cate, which is seldom if ever the case with the ribs of Lioc. apertum. The 

 umbilicus is larger, and the portions of the whorls exposed are somewhat tumid, 

 showing coarse ribs often with the point of bifurcation ; while in Lioc. apertum the 

 whorls of the umbilicus are inclined to be concave, which is due to depression in 

 the inner area, and they possess much smaller ribs (it is almost impossible to 

 delineate these differences in a plate). Lud. rudis has convex and more tumid 

 whorls, with a more distinct carina. Lioc. apertum has compressed whorls with 

 parallel sides, a slightly concave inner area, and a very indistinct carina. Lud. 

 rudis has the ends of its ribs slightly bent forward on the ventral area, and 

 possesses a ventral appendage to the body-chamber. Lioc. apertum has neither of 

 these characters. The inner margin of Lud. rudis is not formed until a later 

 date. It will thus be seen that Lioc. apertum has far more affinities with Lioc. 

 concavum than with Lud. rudis. 



Lioc. apertum occurs in the Concavum-beds at Bradford Abbas, but .cannot 

 be regarded as an abundant shell. When we consider the number of young 

 specimens of the different species of Lioceras and Ludwigia with which it 

 occurs, we cannot be surprised at any difficulty in accurately determining it ; and 

 had I been unacquainted with the large specimen I should have hesitated to 

 describe the species. 



PI. X, figs. 10, 11, represent the largest specimen which I have seen. It 

 was in the cabinet of the late Mr. E. Witchell, F.G.S., who collected it 

 at Bradford Abbas, and very kindly lent it to be figured in this work. As 

 shown by the X the whole of the body-chamber is probably present. The test 

 on the specimen is well preserved, and only allows a small portion of the sutures 

 to be seen. PL XV, figs. 3, 4, show a smaller typical specimen, with most of its 

 very thin test well preserved. This, from Bradford Abbas, is in my collection. PI. 

 XV, figs. 7, 8, illustrate a still younger specimen of the same typical form (prob- 

 ably from Bradford Abbas) to compare with figs. 14, 15. In PL XV, figs. 9, 10, 

 a slight variety, with somewhat thicker whorls and smaller umbilicus, and with the 

 termination of the mouth-border, is delineated. The test on a part of the specimen 

 is fairly well preserved. It came from a small opening made at Bradford Abbas, 

 where the Concavum-beds lay just under the surface, and about a quarter of a mile 

 north of the well-known quarry. The crosses on PL XV indicate the last suture- 

 line, and thus tell us that the body-chamber in this species was a trifle more than 

 is usually possessed by Lioceras, being more than half a whorl in length. 



