TROCHUS. 381 



associated with a slight basal carina which breaks the uniformity of the cone, and 

 thus we gradually pass to another species. In my own Collection these are 

 marked var. " nemoralisP It is quite possible that they are undeveloped forms of 

 Trochus substrigosus, described below. For similar forms see ' Geol. Mag.' vol. cit., 

 pi. iii. 



318. Trochus subldciensis, sp. nov. Plate XXXII, figs. 6 and 7. 



Description (full size) : 



Height . . . . .14 mm. 



Width . . • . .10 mm. 



Spiral angle ..... 40°— 45°. 



Shell regularly conical, not umbilicate. Spire acute, about two-thirds the total 

 height. Number of whorls about seven, perfectly flat, and increasing with complete 

 regularity ; sutures close. The ornaments consist of four thick, tuberculated 

 spirals, each tubercle presenting a squamous appearance, owing to a crescent- 

 shaped hollow on the anterior side. 



In the body- whorl the number of these squamous spirals increases to five and 

 even more ; the anterior spiral is usually deflected away from the base, which is 

 flat and without ornament. Aperture rhomboidal and much depressed. 



Relations and Distribution. — It is extremely probable that there is more than 

 one species amongst these narrow-angled and squamously-ornamented shells, but 

 the state of preservation is scarcely favorable for close discrimination. The spiral 

 angle accords with that of Trochus Luciensis, d'Orb. ; but in that species the 

 spirals are simply nodular, and do not appear to assume the peculiar rope-like 

 character, which enables one to recognise even a fragment of Trochus subluciensis. 



These shells are characteristic of the Murchisonas-zone, occurring in the 

 Oolite Marl of Nails worth, and in the Murchisonse-zone at Stoford and Bradford 

 Abbas ; also on the same horizon in the Irony Nodule-bed at Burton Bradstock. 



A modified form is found in the " Base-bed " at Lincoln, which is also in the 

 Murchisonse-zone. With reference to the Gasteropoda in this bed, it may be 

 observed that their tendency to vary in the direction of bizarre forms is noteworthy. 

 Whether Trochus squamosior, next described, is a species or a " sport " must be 

 left an open question. 



49 



