63 INFERIOR OOLITE AMMONITES. 



The largest specimen of this variety which I have seen measured three inches 

 in diameter. 



Lioceras concavum var. v-sceiptum, 8. Buchman. Plate VI; Plate IX, figs. 1 — 7 ; 



Plate X, figs. 5—8 ; Plate A, 

 fig. 16. 



1881. Ammonites concavus, J. Buckman. Quart. Joura. Geol. Soc, vol. xxxvii, 



p. 60, fig. 1. 



Adult. — Discoidal, compressed, subcarinate ; whorls broad, very slightly convex, 

 with a small concave depression along the inner area, and ornamented with coarse, 

 somewhat indistinct ribs on the outer area, which are continued as lines of growth 

 on the ventral and inner areas. The ribs and lines of growth form sigmoidal 

 curves, being projected on the lateral, recurved, and then slightly projected on 

 the ventral, area. The body-chamber is ornamented merely with very fine lines of 

 growth. The carina is not distinct, but is carried on a sloping ventral area, and 

 scarcely rises above the angle which the two slopes would form if continued ; it is 

 still less conspicuous on the body-chamber, where also the ventral area is flatter. 

 The inner margin is sloped and concave. The inclusion, except at the body- 

 chamber, occupies nearly the whole whorl, forming an umbilicus almost regularly 

 concave, the sides of which are scarcely interrupted by the projection into them of 

 some of the indistinctly-defined margins of some of the inner whorls. The 

 termination to the body-chamber is almost plain, only slightly constricted, and 

 sigmoidal, similar in curvature to the ribs. (The ventral area is somewhat expanded 

 just at the termination). In cases where the test is absent, two well-marked con- 

 strictions, caused by the thickening of the test (PI. IX, fig. 3), are visible on the 

 core ; but they are scarcely perceptible when the test is present. 



Immature. — At a diameter of 16 lines the shell is less compressed; the whorls 

 are convex, with scarcely a distinct inner margin, but sloping towards the centre; and 

 they are ornamented with ribs, which being projected on the lateral area and sharply 

 recurved, are in shape like an expanded <j. These ribs are most conspicuous on 

 the outer area, disappear on the edge of the ventral area, are continued as lines of 

 growth across the carina at right angles, instead of being curved forwards, and 

 are very seldom, if ever, bifurcate. The ventral area is broad and flattened, 

 and carries a very small carina (shown perhaps too distinct in PI. IX, fig. 5). 

 The inclusion is a trifle more than three-fourths of the preceding whorl, leaving 

 the umbilicus somewhat open. This, together with the subsequent increase in the 



