TROCHOTOMA. 445 



Genus — Trochotoma, Deslongcham;ps, 1842. 



" Shell trochiform, conical or depressed ; base iiifundihidiform ; whorls hut sllghtbj 

 convex, heeled ; sinus hand obliterated up to the lip, with the exception of an oblong 

 fissure, chohed in the middle, bipartite; aperture subquadr angular, oblique; lip 

 simple and ivithout slit; columellar lip deeply sunk in the false umbilicus, entire, 

 sinuous'^ — FiscHEE. 



Specimens in our Inferior Oolite, whicli exhibit the more interesting characters 

 of this genus, such as the strangulation of the fissure, and the sinuous or toothed 

 character of the columellar lip, are exceedingly rare. This partly arises from the 

 false umbilicus being plugged up with matrix. The toothed character of the 

 columellar lip is well shown in a specimen of Trochotoma Lindonensis, from 

 Lincoln (PI. XLI, fig. 9). Fischer in 1885 constituted the section, Didymodon, on 

 this feature, the type being Trochotoma quinquecincta, Zieten, from the Corallian 

 of Nattheim, which in many respects resembles the Lincoln specimen. 



The genus Trochotoma in this country is mainly confined to the Lower Oolites, 

 being most abundant in the Bathonian section. The lowest horizons of our Inferior 

 Oolite in Dorsetshire contain some forms which in Normandy are quoted from 

 the Lias, such as Trochotoma gradus. We may admit that T. gradus, T. affinis, 

 and T. calix are little more than varieties of one tabulate form. 



386. Trochotoma calix, Phillips, 1829. Plate XLI, figs. 1 a,l &, variety from the 



Cotteswolds, approaching T. affinis, 

 Deslongchamps ; figs. 6 a, 6 b. 6 c, 

 typical form from the Dogger ; tig. 7. 



1829. SoLAEiUM CALIX, Bean, MS. Phillips, Greol. Yorks., pt. 1, p. 157, pi. xi, 



fig. 30. 

 185-i. Teochotoma calyx, Phillips. Morris, Cat., p. 280. 

 1875. — — — Geol. Yorks., pt. 1, 3rd edit., p. 259. 



1885. — CALIX, Phillips. Hudleston, Geol. Mag., dec. 3, vol. ii, 



p. 156, pi. iv, figs. 6, 6 «, 6 h. 

 Non Pleueoxomaeia calix, (VOrbigny. Terr. Jur.,vol. ii, p. 476, pi. ccclxxxiii, 



figs. 6, 7. 



Bibliography, 8fc. — On the view that we should separate T. calix from T. gradus 



and T. affinis, the synonymy given by me in the ' Geol. Mag.' is too comprehensive. 



The type specimen of Solarium calix is not, I believe, to be found at York, 



59 



