TROCHUS. 387 
Bibliography, §c.—According to Tawney (op. cit.), Oppel, and after him 
Brauns, identified Miimster’s species with 7. monilitectus, Phil., but for this 
identification there is clearly no warrant. I cannot follow Tawney in regarding 
this species as a Littorina. 
Description : 
Height. : é : . 12:5 mm. 
Width : : : : . 10°5 mm. 
Spiral angle 2 ake, 
Shell conical, not ambileated, aiahtly darveted: Spire nearly two-thirds the 
total height; spiral angle sometimes rather obtuse. Number of whorls seven, 
separated by a very wide suture. Those at the extreme apex are smooth, but 
all the principal whorls are concave, and bounded by tuberculated spiral belts at 
the posterior and anterior margins. 
The body-whorl, which is separated from the spire by a very wide suture, is 
similar in shape and ornament, but carries a third keel at the angle of the shells, 
the third one being the least prominent. Base nearly flat and spirally ornamented. 
Aperture subrhomboidal and depressed. 
Relations and Distribution—Regarded as a Trochus this species stands pretty 
well alone. 1. biarmatus, M., differs from English specimens in having the third 
keel exposed in the whorls of the spire—always supposing the enlarged figure of 
Goldfuss to be an accurate representation. T'rochus bitorquatus, Héb. and Desl., 
greatly resembles our Inferior Oolite specimens. 
Trochus biarmatus with us is essentially a fossil of the Parkinsoni-zone or of 
the beds immediately below. The most northerly point noted is Notgrove. At 
Horton Hill it is abundant and well developed. The best specimens come from 
Grove and Woolston (Castle Cary district). It is met with in the Parkinsoni- 
mar! of Bradford Abbas; also at Stoford, and in the Parkinsoni-zone of South 
Dorset. 
327. TrocHus MakGA, sp. nov. Plate XXXII, fig. 15. 
Description : 
Height : : ; : 7 O mim. 
Spiral angle . 4 : 59° 
Shell conical, imperforate. Spire alavated anal. acute with a slightly obtuse 
apex. Number of whorls six; slightly concave, with a considerable anterior 
prominence. Body-whorl very concave with a blunt carina at the angle. The 
entire shell is ornamented by fine spiral striaw, closely set, and faintly decussated 
