Trochus. 
MOLLUSCA. 
75 
and its base truncated in some species; operculum horny, 
circular, and spiral, with many close-set volutions, and 
an external spiral line outside, frequently covered with a 
horny epidermis. 
1. T. duplicatus. — The Two-plaited Trochus, pi. 
XXXIX. fig. 1, 2. 
Trochus duplicatus. Sowerby, Min. Conch. II. p. 181, pi. 
182, fig. 5. Fleming, Brit. An. p. 324. 
Shell conical, shining; spire consisting of four volutions, 
with plain, concave sides, a single projecting crenulated fillet 
on the upper edge, and a double crenulated spiral Carina round 
the base of each; base with an open umbilicus, the margin of 
which is beset with about seven, somewhat prominent tuber¬ 
cles ; aperture quadrangular. 
Found in the Inferior Oolite at Little Sodbury. 
2 . T. Gibsii —Gibs’ Trochus, pi. XXXIX. fig. 3, 4. 
Trochus Gibsii. Sowerby, Min. Conch. III. p. 139, pi. 278, 
fig. 1. Fleming, Brit. An. p. 325. 
Shell conical, short, wider than high; spire with four or five 
volutions, flattened on the sides, with obtusely carinated edges, 
on their upper parts a concentric, elevated spiral band, which is 
crossed by curved striae; base convex, furnished with concentric 
and radiating striae, producing a fine reticulated appearance; 
umbilicus large, and almost smooth; aperture rhomboidal; inner 
lip somewhat reflected over the base of the columella, but not 
encroaching upon the umbilicus. 
The semicircular striae on the concentric band seems to indicate 
a sinus in the outer lip of the perfect shell. 
Found in the Chalk Marl, or Pyritifcrous Clay, at Folkstone. 
3. T. dimidiatus.— The Divided Trochus, pi. XXXIX. 
fig. 5. 
Trochus dimidiatus. Sowerby, Min. Conch. II. p. 181, pi. 
181, fig. 4. Fleming, Brit. An. p. 324. 
Shell conical, surface rough, and free from polish; body 
volution flat on the sides, and concave above, with an entire 
carina in the centre; superior volutions convex; base convex, 
and provided with a carinated margin; aperture pentangular; 
columella straight, and solid. 
Found at Little Sodbury, in the Inferior Oolite. 
4. T. concavus —The Concave Trochus, pi. XXXIX. fig. 
6, 7. 
Trochus concavus. Sowerby, Min. Conch. II. p. 180, pi. 
181, fig. 3. 
Shell conical; spire consisting of three spirally striated volu¬ 
tions, with concave sides, where it is provided with a slightly 
developed row of tubercles, and the lower margin of each cari¬ 
nated; base smooth, destitute of an umbilicus; its diameter 
being somewhat more than its height; aperture acutely rhom¬ 
boidal. 
Found in the Inferior Oolite, Little Sodbury. 
Distinguished from the T. duplicatus by its spiral striae. 
5. T. similis. —The Similar Trochus, pi. XXXIX. fig. 
8 , 9, 
Trochus similis . Sowerby, Min. Conch. II. p. 179, pi. 181, 
fig. 2. Fleming, Brit. An. p. 324. 
Conical; spire consisting of four flat-sided volutions, the base 
of each projecting slightly over that under it; all of them 
provided with numerous transverse, variously-sized ridges, en¬ 
larging as they descend, the lower and largest with minute 
intervening ones; several of the ridges on each volution are 
granulated, between each of which are small plain ones. 
Found in the Crag at Holywell. 
G. T. dubius. —The Doubtful Trochus, pi. XXXIX. fig. 10. 
Trochus - ? Mantell, Geo. of Sussex, p. 109, pi. 18, 
fig. 7. 
Shell smooth, subconic; spire occupying nearly half the 
length of the shell, and consisting of three moderately inflated, 
well defined volutions ; base rounded. 
Found in the Grey Chalk Marl at Ilamsey, Sussex. 
7. T. Mantelli.— Mantell’s Trochus, pi. XXXIX. fig. 11. 
Trochus agglutinans ? Sowerby, Min. Conch. I. p. 224, pi. 
223, smaller figs. Trochus - ? Mantell, Geo. of Sussex, p. 
109, pi. 18, fig. 9* Lamarck, Foss, des Env. de Paris, p. 102. 
Trochus umbilicaris, Brander, Foss. Hant. p. 10, pi. 1, fig. 
4, 5. 
Shell depressed, discoidal, with a slightly convex base, a pli¬ 
cated, wide and shallow, scolloped umbilicus, and its margin 
acutely angular; aperture oblong. 
Found at Ilamsey, Sussex; and Barton Cliff. 
8. T. Tiara. —The Tiara Trochus, pi. XXXIX. fig. 12, 13. 
Trochus bicarinatus. Sowerby, Min. Conch. III. p. 39, pi. 
221, fig. 2. Trochus Tiara , Fleming, Brit. An. p. 325. 
Shell subconic, subdepressed; body large; spire small, with 
divergent furrows and ridges; volutions with two obscure 
carina^; body spirally striated; base produced, concentrically 
striated, and provided with a wide and deep umbilicus. 
Found in the Green Sand at Marsham Field, near Oxford. 
9. T. fasciatus. — The Banded Trochus, pi. XXXIX. fig. 
14. 
Trochus fasciatus. Sowerby, Min. Conch. III. p. 37, pi. 
220, fig. 1. Fleming, Brit. An. p. 324. 
Shell conical; body large; spire of medium length, consisting 
of six or seven well divided, somewhat convex volutions, with a 
spiral band round the centre of each; base rather flattened, its 
diameter nearly equal to the height of the shell; whole external 
surface covered with rather wide longitudinal and spiral striae; 
the latter being the most prominent, and the longitudinal ones 
diverging from the central band in both directions; aperture 
large, quadrangular; columella with a single plait upon it. 
Found in the Inferior Oolite at Dundry. 
10. T. monilifer. —The Necklace Trochus, pi. XXXIX. 
fig. 15, 16. 
Trochus monilifer. Sowerby, Min. Conch. III. p. 91, pi. 
367- Fleming, Brit. An. p.325. Trochus nodidosus, Brander, 
Foss. Hant. p. 10, pi. 1, fig. 6. 
Conical, sides nearl) flat; body occupying about a third of 
the length of the shell; volutions but slightly produced, each 
provided with three spiral rows of tubercles, and having the 
lower edges crenated; base a little convex, its diameter about 
equal to the height of the shell, and provided with six rows of 
regularly set granules, its centre smooth; aperture quadrangular, 
and placed obliquely, its margin entire and undulous, inside 
pearlaceous; columella truncated, and lying along *the inner 
margin of the aperture. 
Found in the London Clay at Hordwell, where it was dis¬ 
covered by Miss Teed. 
