TURBO (MONODONTA). 357 



towards the anterior extremity, so as to produce a denticulated appearance 

 succeeded by a kind of notch. 



Relations and Distribution. — Although there is much in this curious little shell 

 to remind one of Brachytrema, I think we must regard it as a member of the 

 Turbinidge. The form (fig. 18) may represent an aged specimen, or possibly 

 another species. It bears some resemblance to Monodonta exigua, Lycett (' Suppl./ 

 p. 22, pi. xliv, fig. 29), from the Great Oolite. 



Monodonta pisolitica is fairly plentiful in the Pea-grit at Leckhampton. 



292. Monodonta Lyellt, d'Archiac, 1843. Plate XXX, figs. 1 and 2 ; var. 



humilis, fig. 3. 



1843. Monodonta Lyelli, d'Archiac. Mem. Soc. Geol. France, vol. v, pt. 2, 



p. 380, pi. xxix, figs. 8 and 8 a ; id., 

 var., 8 b, 8 c. 



1850. Turbo Lyelli, d'Orb. Prod., i, p. 301. 



1851. Monodonta Lyellii, d'Arch. Morris and Lycett, Great Ool. Moll., pt. 1, 



p. 67, pi. xi, fig. 4. 

 1853. — — — Morris, Quart. Journ. Geol. Soc, vol. ix, 



p. 326. 

 1884. — Lyelli, d'Arch. Cossmann, fitage Bath., p. 271, pi. vii, 



figs. 28, 29. 



Bibliography, Sfc. — We have the authority of Morris as to the occurrence of 

 this well-known Bathonian species in the Lincolnshire Limestone, where the forms 

 differ somewhat from those in the Great Oolite of Minchinhampton, and possibly 

 still more from d'Archiac's types. It seems to be an eastern form, being quoted 

 from the Bathonian and Bajocian of Eastern France. 

 Description : 



Height of average specimen . . .8 mm. 



Width . . . . .7 mm. 



Mean spiral angle .... 65°. 



Shell turbinate, subumbilicate ; spiral angle fairly regular, but with a flattened 

 apex ; sutures wide and canaliculate. Number of whorls four, the two at the apex 

 smooth, the other two ornamented with from three to four tuberculated spirals, 

 the tubercles having a shallow concave pit on the anterior side. 



The body-whorl is subventricose, more or less carinated, and carries three 

 strongly tuberculated spirals on the side, and a fourth, with lesser tuberculations, 

 at the angle. Four more tuberculated spirals ornament the base, including the 

 umbilical cavity, the margin of which is fringed by the one carrying the strongest 



46 



