374 GASTEROPODA OF THE INFERIOR OOLITE. 



more than half the total height. Number of whorls seven ; sides concave, the 

 posterior and anterior margins decorated by nodular carinae. A wide and regular 

 suture separates the lower carina of one whorl from the upper carina of the next ; 

 the intercarinal spaces have no spiral ornamentation, but very fine axial lines may 

 be seen on the glabrous surface. 



The body-whorl is similar, but with a double nodulated carina round the base, 

 which is flat and smooth, but rises towards the centre, where an umbilicus of 

 moderate width and depth is girdled by a set of large tubercles, about eight in 

 number. Aperture subrhomboidal and depressed. 



Relations and Distribution. — This species is, perhaps, the most abundant 

 Gasteropod in the Upper Division of the Inferior Oolite, being especially charac- 

 teristic of the ParJcinsoni-zone from Burton Bradstock as far north at least as 

 Aston in the Cotteswolds. I have no specimens either from the Lincolnshire 

 Limestone or from Yorkshire. It is essentially a Bajocian (i. e. Upper Division) 

 form, being abundant at Bayeux, &c. French specimens seem to be rather 

 wider-angled than ours. There is a marked variety from Powerstock in Dorset, 

 which I have not figured. 



This is very different to the polymorphous species usually known as Trochus 

 subduplicatus, d'Orb., from the Lower Beds, but is closely related to the two forms 

 next described. 



311. Teoohus angulatus, Soioerby, 1817. Plate XXXI, fig. 11. 



1817. Teochus concavus, Soioerby. Min. Conch., pi. clxxxi, fig. 3 ; op. cit., 



vol. iv, index aud corrigenda, 1823, as 

 Teochus angulatus. 



1854. — angulatus, Sow. Morris, Cat., p. 281. 



This form is somewhat wider than average specimens of T. duplicatus, of which it 

 may, to a certain extent, be considered a glabrous variety. Sowerby relied upon 

 the presence of a few transverse striae as helping to separate it. Though this test 

 fails, the following important differences may be noted, viz. the extreme smooth- 

 ness of the shell, the absence of umbilicus, and the fusion of the two keels 

 into one. 



Intermediate forms which show the connection, but which incline more towards 

 T. duplicatus, occur in several places. Specimens, such as the one figured, 

 are rare. 



