66 INFERIOR OOLITE AMMONITES. 



able to satisfy myself concerning the young specimens of this variety, but I 

 should expect that they would prove difficult to separate from Ludwigia cornu. 

 The umbilicus, however, is much smaller ; the shell is more compressed on the inner 

 area and not so much on the outer (that is, it is not so much flattened) ; the ribs, 

 which are inconspicuous, though somewhat broad — generally giving a rather 

 smooth appearance to the adult shell, — are straighter on the inner area, are not so 

 numerous, and are more curved on the outer area. The best distinction lies in the 

 ventral area and carina. Ludwigia cornu is carinate, that is, the ventral area slopes 

 but slightly, and the carina stands up prominently and distinctly. Lioc. formosum, 

 and in fact Lioc. concavum generally, no matter how trenchant the carina may seem, 

 can only be called sub-carinate, because the ventral area slopes very much, and the 

 carina is little more than a compression of the two edges of that area. The suture- 

 lines, when visible, are a good guide. A specimen of this variety exhibits a true 

 Lioceras suture-line (PI. A, fig. 15, p. 123) ; the chambers are close together, with 

 regularly decreasing lateral lobes, and with at least four well-marked auxiliary lobes. 



It might almost be said that this variety can be separated with more ease from 

 the typical Lioc. concavum than from Ludioigia cornu, because one does not require 

 to find so much difference. The ribs more obscure, the inner area more depressed, 

 a shallower and more open umbilicus with more sloping walls, and the inner whorls 

 rather more exposed, are the characters which separate it from the type. 



This variety comes with the type in the Concavum-beds of Bradford Abbas, 

 Dorset, and seems to be scarce. 



The beautiful specimen which has been figured (PI. X, fig. 1,2) is by far the best 

 I have seen. The test is perfect on one side, and is extremely well preserved on 

 the ventral area ; while the termination is unusually complete on both sides, only a 

 small portion of its test on one side being absent. The specimen was in the 

 collection of my very kind friend, the late Mr. E. Witchell, F.G.S., who was always 

 so ready to assist me in every possible manner with the most untiring good-nature. 

 He lent me this specimen for figuring in this work, and Mrs. Witchell generously 

 allowed me to add it to my own collection. Plate A, fig. 15, shows the suture-line 

 taken from a specimen also in my collection. It is noticeable because of the absence 

 of any of the larger digitations on the sides of the lobes. 



Lioceras concavum, var. pingue, 8. Buchnan. Plate XII, figs. 1, 2. 



Discoidal, somewhat compressed, subcarinate ; whorls thick, with almost flat- 

 tened sides showing the depression in the inner area, and very slightly ornamented 

 with fine sigmoidal radii, which are projected forwards considerably on both the 



