LIOCERAS FORMOSUM. 65 



beds may be absent at Bradford Abbas. Judging, however, from certain Ammonite- 

 species collected by my father, I should expect to find these beds well developed 

 at Sherborne in the Sandford-Lane quarry; but unfortunately it has not been 

 worked down to this level for many years. I have therefore thought it preferable, 

 when treating of the chief fossil-bed of Bradford Abbas and its vicinity, to 

 use Mr. Hudleston's term " Concavum-beds " for the horizon of which the species 

 is characteristic. I much wish that we could see a good exposure at Sherborne 

 down to the Yeovil Sands at any point where the Humphriesianum-zone is 

 developed, because it would probably help us to thoroughly clear up some diffi- 

 culties which still exist in the correlation of the Inferior-Oolite strata. The 

 position of the Concavum-beds in the Bradford- Abbas district can be seen to be 

 just above the thin bed containing Ludrvigia Murchisonce ; and in my opinion they 

 are the equivalents of the Gryphite- and Lower Trigonia-grits of the Cotteswold 

 area. 1 A position equivalent to that of the former my father always assigned 

 them ; but, not taking sufficient account of the presence at Bradford Abbas of the 

 Murchisonce-zone below, he had recourse to the Yeovil Sands to supply the 

 deficiency, that is, in correlating the Oolite-marl and Pea-grit series of the Cottes- 

 wolds with the Dorset strata. 2 



Lioceras concavum, var. formosum, 8. Buchman. Plate X, figs. 1,2; Plate A, fig. 15. 



Discoidal, much compressed, subcarinate ; whorls sub-convex with much 

 depressed inner portion, and ornamented with broad but inconspicuous ribs, more 

 falciform than sigmoidal. The ribs are, correctly speaking, not bifurcate, but 

 some, intermediate, appear on the outer, and are not visible on the inner, area. 

 Ventral area acutely sloping to a small carina, which is continued, though less 

 conspicuously, to the end of the body-chamber. Inclusion extending over almost 

 the whole of the preceding whorl. Inner margin scarcely concave, but much sloped. 

 Umbilicus shallow, on account of the depression of the inner area, and open, on 

 account of the marked slope of the inner margin. Termination of body-chamber 

 plain, sigmoidal, with a strong bend forwards on the ventral area, where it is 

 bluntly pointed. When the test is absent, the core shows, just before the end of 

 the mouth, the usual furrow, due to the extreme thinness of the test at the 

 outermost edge, and its rather quick thickening on the inside. 



This variety of Lioc. concavum is chiefly noticeable for its resemblance to the 

 typical form of Ludwigia comu s depicted in Plate IV, figs. 3, 4. I have not been 



1 See p. 91. 



2 " On the so-called Midford Sands," ' Quart. Journ. Geol. Soc.,' vol. xxxv, p. 738, 1879. 



3 It was to the form with the smaller umbilicus that I first gave the name, and therefore I 

 consider that as the type. 



9 



