TROCHUS. 385 
a rather close suture in the early stage, which becomes wider ; six or seven fine 
granular spirals ornament the whorls of the spire, the posterior and anterior 
spiral being slightly the most prominent in some cases, so as to form slight belts 
in the neighbourhood of the suture. 
In the body-whorl, which is rather tumid, the ornaments become irregular 
with a tendency to effacement of the spiral lines, but there is often a marked 
bicarination at the angle of the shell; the angle is rounded off into a full 
base, which is marked by fine wavy spiral striz. Growth-lines decussate the 
general ornamentation and are very conspicuous where the spiral lines fail. 
Aperture subquadrate with some thickening of the inner lip. 
Relations and Distribution.—Trochus substrigosus is a truly polymorphous shell, 
and when, it develops an additional whorl, we have some difficulty in believing 
that the species is the same—in other words, that fig. 4 and fig. 11 are different 
conditions of the same species. 
The more perfect form (fig. 11) occurs sparingly in the Parkinsoni-zone of 
Bradford Abbas and Burton Bradstock. Fossils from the Cornbrash of 
Scarborough exhibit a similar polymorphous tendency. 
324. Trocnus Burronensis, Lycett, 1863, Inferior Oolite variety. Plate XXXII, 
fig. 12. 
1863. Trocuvus Burronensis, Lycett. Suppl., p. 99, pl. xlv, fig. 16. 
Description : 
Height : : 4 ; . 13 mm. 
Width ; : , : . 13 mm. 
Spiral angle : am EGO: 
Shell regularly conical, imperforate. Spire elevated, acute; sutures close. 
Number of whorls seven, flat and without ornament. Sometimes one of the 
whorls overhangs a little, otherwise there is hardly any break in the outline of a 
perfect cone. There is a slight keel at the base of the body-whorl. Base nearly 
flat and smooth. Aperture subrhomboidal and depressed, with a considerable 
columellar callus. 
Relations and Distribution.—One would imagine that there should not be much 
difficulty in finding a name for this perfectly smooth and regularly conical shell. 
Trochus Halesus, d’Orb., presents some features of resemblance, but M. Cossmann 
regards that species as an Ataphrus rather than a Trochus. Again Trochus Actzxa, 
d’Orb., has a resemblance, yet we miss the “bourrelet”’ characteristic of that 
species. The Inferior Oolite fossil figured in the accompanying plate differs from 
