Trochus. 



MOLLUSCA. 



75 



I 



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 dupUcatus. 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. I. 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 stria-, producing a fine reticulated appearance; 

 umbilicus large, and almost smooth; aperture rhomboidal; inner 

 Up somewhat reflected over the baise of the columella, but not 

 encroaching upon the umbilicus. 



The semicircular stride on the concentric band seems to indicfate 

 a sinus in the outer lip of the perfect shell. 



Found in the Chalk Marl, or Pyritiferous 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. dupUcatus by its spiral stria:. 



5. T. siMiLis The Similar Trochus, pi. XXXIX. fig. 



S,9, 



Troihus 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. 



6. 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 Hamsey, Sussex. 



7. T. Mantelli.— MantcU's Trochus, pi. XXXIX. fig. 11. 

 Trochus agglutivans ? 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 Hamsey, Sussex ; and Barton Cliff. 



8. T. TiABA.— 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 

 carinse ; 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 nodulosus, Brander, 

 Foss. Hant. p. 10, pi. 1, fig. 6. 



Conical, sides nearly 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. 



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