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 striae 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 PI. 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 Murchisonas-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. Pleorotomaria (Leptomaria) monticulus, Deslong champs, 1848. Not figured. 



184S. Pleurotosiaria monticulus, Deslong champs. Vol. cit., p. 143, pi. xiii, 



figs. 5 a — d. 



1854. — — — ? D'Orbigny, Terr. Jur., 



vol. ii, p. 485, pi. ccclxxxviii, 

 figs. (3—10. 



1873. — — PTawney, Dundry Gas- 



teropoda, p. 44 (30). 



The specimen on which Tawney based this identification has more resemblance 

 to PI. Agathis, Desl. Lately, however, Mr. Wilson has found a specimen at Dundry, 

 which, though rather small, may be safely identified with PL monticulus. 



351. Plkurotomaria monticuloides, sp. nov. Plate XXXV, figs. 10, 10 a. 



Description : 



Height . . . . .27 mm. 



Basal diameter . . . .29 mm. 



Spiral angle (subconvex) . . . 70°. 



Shell conoidal, moderately umbilicate. Spire subconvex, apex rather obtuse. 



