PLEUROTOMARIA. 413 
earlier whorls its position is so anterior as to be almost concealed. The body- 
whorl is relatively large, convex, and rounded off at the basal periphery, the 
whole being ornamented with regular spiral striz up to the edge of the umbilicus ; 
in this portion of the shell the sinus-band is about two-thirds down. Aperture 
subdepressed and oblique. 
Obconical Variety (fig. 9).—This presents certain analogies with the variety 
described under the preceding species. Usually specimens run rather larger than 
in the more depressed and typical form of Pl. Ajax; spiral angle in some cases 
as low as 80°, always obtuse. The sinus-band is less concealed in the earlier 
whorls, and also more prominent and striated. There are also other differences. 
Relations and Distribution.—Pl. Ajax, including the obconical variety, is 
rather abundant in the bottom bed of the Lincolnshire Limestone at Lincoln, 
which is in the Murchisonz-zone. It seems to be a representative of Pl. sulcata, 
which occurs on the same horizon in the south-west; the chief difference lying in 
the regular and more deeply incised spiral ornamentation and the smaller 
umbilicus. There is a somewhat similar form in the Northampton Sand at 
Duston. 
350. PLevroromarta (Leptomaria) monticuLus, Deslongchamps, 1848. Not figured. 
1848. PrievRroromarta Monticunus, Deslongchamps. Vol. cit., p. 148, pl. xiii, 
figs. 5 a—d. 
1854. = _ -- ? D’Orbigny, Terr. Jur., 
vol. ii, p. 485, pl. eeelxxxviii, 
figs. 6—10. 
1873. _— _- — ? Tawney, Dundry Gas- 
teropoda, p. 44 (36). 
The specimen on which Tawney based this identification has more resemblance 
to Pl. Agathis, Desl. Lately, however, Mr. Wilson has found a specimen at Dundry, 
which, though rather small, may be safely identified with Pl. monticulus. 
351. PLEUROTOMARIA MONTICULOIDES, sp. nov. Plate XXXV, figs. 10, 10a. 
Description : 
Height : : : : 2 27 mm. 
Basal diameter ‘ ; ; . 29 mm. 
Spiral angle (subconvex) : Std0e: 
Shell conoidal, moderately umbilicate. Spire subconvex, apex rather obtuse. 
