TROCHUS. 387 



Bibliography, Sfc. — According to Tawney {op. cit.), Oppel, and after him 

 Brauns, identified Minister's species with T. monilitectus, Phil., but for this 

 identification there is clearly no warrant. I cannot follow Tawney in regarding 

 this species as a Littorina. 



Description : 



Height ..... 125 mm. 

 Width ..... 10-5 mm. 



Spiral angle .... 52°. 



Shell conical, not umbilicated, slightly turreted. 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. T. 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. Trochus bitorquatus, Heb. and Desl., 

 greatly resembles our Inferior Oolite specimens. 



Trochus biarmatus with us is essentially a fossil of the Parkins oni-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 Parlcinsoni- 

 marl of Bradford Abbas ; also at Stoford, and in the Parkinsoni-zone of South 

 Dorset. 



327. Trochus marga, sp. nov. Plate XXXII, fig. 15. 



Description : 



Height . . . . .6 mm. 



Width . . . . .5 mm. 



Spiral angle . . . . .52°. 



Shell conical, imperforate. Spire elevated and 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 strise, closely set, and faintly decussated 



