152 GASTEROPODA OF THE INFERIOR OOLITE. 
shorter, and to be more coarsely ornamented in the zones of Am. Humphriesianus 
and Parkinsont. 
Description of var. spinicostata : 
Length of a fair-sized specimen 5 . 39mm. 
Width . ; : : . 75 mm, 
Ratio of body-whorl to entire length . sy odlee OO: 
Spiral angle ; : H se LY, 
Shell elongate, strongly turrited. Spiral angle nearly regular; whorls about 
fifteen in number, subconvex in the apical region, but becoming flatter and 
somewhat pinched anteriorly so as to increase the turriting of the shells. The 
ornaments consist of about eight fine spiral lines, which in the latter whorls 
assume the character of spiral belts, with a considerable interspace ; subordinate 
spiral lines may be detected, especially in the more mature whorls. The upper- 
most one is strongly tuberculate at the points of intersection with the cost, 
which are numerous. The coste are rather fine, and extend from suture to 
suture, decussating with the spirals so as to present a somewhat granular appear- 
ance at the points of intersection. 
The body-whorl is less than one third the entire length of the shell, the shape 
and ornamentation are similar in character to the whorls of the spire, with, 
however, a tendency for the costee to become more arcuate. The base is tolerably 
full and marked with strong spiral striae, which are partially decussated by a faint 
continuation of the coste. The aperture is ovate-elongate ; the outer lip thin 
(always broken away). There exists a kind of rudimentary posterior canal. 
Columella excavated and but slightly encrusted. Anterior canal considerably 
produced, but slightly reflexed. 
The following sub-varieties may be noted. Fig. 8 6 is less subulate, and 
shorter. The specimen figured has suffered slightly from wear or solvents, so that 
the spiral lines are less distinct. The costs are scarcely decussated in conse- 
quence. This is a medium-sized specimen and greatly resembles some of the 
larger forms of C. subscalariforme from the Bayeux-beds. Fig. 8 ¢ represents a 
very elongate form, with fine ornamentation. In Fig. 8d the proportions are as 
usual, but that which constitutes some difference is the twist in the coste, and 
their marked inclination from right to left. In this specimen the spiral lines on 
the cost are entirely obliterated. In Fig. 8e the coste are stouter and less 
numerous than usual, with great salience of the spinous row of nodules on the 
shoulder of each whorl. The traces of spiral ornamentation are still more difficult 
to find. This sub-variety leads up to Cerithiwm subglabrum. 
Relations and Distribution.—The most typical forms of C. spinicostatum are to 
be met with in the Sowerbyi-bed of Bradford Abbas, where it is one of the most 
abundant fossils, though not always in the best state of preservation. It 1s 
