PLEUROTOMARIA. 
287 
Trochus Bouei, Steininger,^ is figured from an Bifel shell without description, 
and is hardly identifiable. It has almost the shape of an equilateral triangle, with 
one row of large separate tubercles on each of the upper whorls, and about six 
rows on the body-whorl. At all events it differs from the present shell in being 
strongly tuberculate. 
I have employed the classic form of the word " Newton " for the name of this 
species. 
7. Pleurotomaria trochoides, Whidborne. PI. XXVII, figs. 17 — 19. 
1841. Pleubotomaeia monilifeea, Phillips. Pal. Foss., p. 97, pi. xxxvii, fig. 
178 (not Geol. Yorks.). 
1842. — — d'Arch. and de Vern., Greol. Trans., ser. 2, 
vol. vi, pt. 2, p. 389. 
1854. — — Morris, Catal. Brit. Foss., p. 273. 
1888. — — Etheridge. Foss. Brit., vol. i. Pal., p. 164. 
1889. — TEOCHOiDES, Whidborne. Geol. Mag., dec. 8, vol. vi, 
p. 30. 
Descriptio7i. — Shell small, trochiform, acuminate, of six or eight narrow 
volutions. Apex very small and slightly rounded. Spire conical, elevated, with 
slightly concave sides caused by the greater dilation of the lower whorls ; 
sometimes a little bent on one side. Suture very deep, excavate, and rounded. 
Whorls spreading out obliquely and straightly to the elbow, which is nearly at the 
bottom of the whorl, and then turning through a sharp angle to form a flattish 
oblique base. Ornament generally coarse, consisting of two beaded spiral ridges 
immediately below the suture, followed by a wide, flat, or slightly concave median 
area or groove, which is smooth or filled with fine threads, then by a broad 
elevated sinus-band on the widest part, then by another groove bounded by a flat 
ridge, and then by numerous finer close ridges on the base ; the surface being 
thus divided into two prominences and two grooves. Transverse ornament con- 
sisting of strong ribs, which cross and tuberculate the upper ridges in a forward 
direction, then, becoming much finer, sweep back across the median groove, then 
become perpendicular and sometimes very strong in the sinus-band, then tend 
forward in the groove below it, and then form a sigmoid curve on the base. 
Sinus-band bounded by two very strong prominent ridges. Mouth apparently 
trapezoidal, produced in front. Columella thick, arched. Shell-structure thick. 
No umbilicus. 
' 1834, Steininger, 'Mem. Soc. Geol. Fr.,' vol. i, pt. 2, p. 371, pi. xxiii, fig. 4. 
