436 GASTEROPODA OF THE INFERIOR OOLITE. 



salient, and between these lies the sinus-band. Base subconvex, with a marginal 

 furrow, and spiral lines decussated by strong radii. Umbilicus wide and deep, 

 exhibiting the inner coil of the whorls. 



Varieties. — Specimens, such as fig. 5, present some modifications of ornament 

 with a higher spire. These seem to connect with PL Aglaia, d'Orb. (vol. cit., 

 p. 469, pi. ccclxxxi, figs. 1 — 5). There is also another form (not figured) from 

 the Murchisonse-zone of Bradford Abbas, which may possibly represent a variety 

 of this species. This latter I have hitherto considered to represent an early 

 stage of PL actinomphala on a lower horizon. 



Relations and Distribution. — Closely related to PI. actinomphala, the position 

 of PI. Baugieri both in France and in England lies in the Lower Division of the 

 Inferior Oolite. Nearly all my specimens are from the Murchisonae-zone of 

 Bradford Abbas. 



377. Pleubotomaeia mopsa, d'Orbigny, 1850. Plate XXXIX, figs. 6 a, 6 b, 6 c. 



1850. Pleubotomaeia mopsa, d'Orbigny. Prod., i, p. 230. 



1854. Terr. Jur., vol. ii, p. 421, pi. cccliv, 



figs. 6—10. 

 Syn. — Debuchii, var. exsertiuscula, Deslongchamps. Vol. 



cit., p. 93, pi. xv, fig. 10. 



Bibliography , 8fc. — So many forms were grouped by Deslongchamps under the 

 " species " named Debuchii that d'Orbigny concluded to break it up. PI. Debuchii 

 and all its varieties are mainly Liassic, but traces of some of them certainly occur 

 in the Lower Division of the Inferior Oolite. 



DfsrrijitioH : 



Height . . . . .13 mm. 



Basal diameter . . . .27 mm. 



Spiral angle ..... 140°* 



Shell subdiscoidal, largely umbilicate. Spire low but regular. Whorls (six) 

 increasing by steps, angular and carinate, posterior areas tabulate and wide, ante- 

 rior areas sloping at an angle of 60°; suture canaliculate. The flat part of the 

 whorls is ornamented by three (in the body-whorl sometimes four) raised tubercu- 

 lated spirals, the outermost occupying the keel (in the body-whorl the nodules are 

 fused into an appearance of radial costas) ; the anterior sloping area is decussated, 

 but more than half its total width is occupied by the sinus-band. 



The sinus-band is wide, flat, and rather receding ; it is margined above and 

 below by a spiral line, with a single central line decussated ; in the last whorl it 

 occupies a position between the nodulated keel and the more prominent basal 



