TROCHUS. 389 



Description .• 



Height . . . . .8 mm. 



Width . . . . .6 mm. 



Spiral angle (about) .... 60°. 



Shell conoidal, imperforate ; spiral angle obtuse with a rather sharp apex. 

 Number of whorls about five, moderately convex, sutures close ; the ornaments 

 consist of very numerous, fine, spiral lines, with but faint traces of radial 

 decussation. The body- whorl is about half the entire height, and slightly 

 compressed anteriorly so as to be well within the spiral angle. The spiral lines 

 are extremely numerous, and one, a little more elevated than the rest, forms a 

 slight keel at the angle of the whorl ; this angle is rounded off into the very full 

 base, which is similarly striated. The aperture is suborbicular and rather 

 restricted, without the least trace of an umbilical or columellar furrow. 



Specimens from Lincoln are similar, except that the base is rather more 

 rounded off and there is a slight " monodontoid " appearance on the columel a. 



Relations and Distribution. — This peculiar form seems to stand by itself in our 

 Inferior Oolite, occurring in the Murchisonse-zone at two widely separate localities, 

 viz. at Lincoln in the " Base-bed," and at Burton Bradstock in the Irony 

 Nodule-bed. 



331. ? Trochus bicingendus, Lycett, 1850. Plate XXXI, fig. 15. 



1850. Trochus bicingendus, Lycett. Ann. Mag. Nat. Hist., 2nd ser., vol. vi, 



p. 416; and Proc. Cotteswold Nat. Club, 

 vol. i, p. 77. 



The following is the author's diagnosis : — " Elevated whorls rather concave, 

 with two encircling nodose ribs, one at each margin of the whorl, and three 

 mesial circles of nodules." 



The type, which is in the Jermyn-Street Museum, measures : — Height 8 mm., 

 width 4-5 mm., spiral angle 45°. From the Inferior Oolite of the Cotteswolds. 



It seems probable that Trochus bicingendus represents the early stage of a shell 

 from the Pea-grit of Longfords, represented in the present work (PI. XXIV, fig. 7), 

 and which was correlated (p. 301) with Littorina recteplanata, Tawney. If this 

 correlation be correct, it would seem proper to substitute Lycett's specific name ; 

 but, since there is a doubt, we must retain both names for the present. 



It is quite likely that I have not succeeded in enumerating every species of 

 fossil shell from our Inferior Oolite entitled to the name of Trochus. For 

 instance, there is T. clypeatus, Witchell (' Proc. Cotteswold Nat. Club,' vol. vii, 

 p. 128, pi. iv, fig. 3), which I have not seen; though, to judge from the figure 

 and description, it is most probably identical with Trochus dimidiatus, Sow. 



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