PLEUROTOMARIA. 4.07 
Relations and Distribution.—Closely related by its concave spire and general 
character to the two preceding species, Pl. Bessina and its numerous varieties 
represent the most wide-angled forms of the mutabilis-group. In this country it 
is essentially a fossil of the Parkinsoni-zone, and is not uncommon in that horizon 
at Halfway House. 
342. Pievrotomaria Dunprignsis, Tawney, 1873. Plate XXXIV, fig. 11. 
1873. Prevrotomaria DunpRiensis, Tawney. Dundry Gasteropoda, p. 46 (88), 
pl. i, fig. 3. 
Description : 
Height : ; : : = 27 mm 
Basal diameter : : : . 32mm. 
Spiral angle . , : a okt 
Shell regularly conical and moderately umbilicated. Whorls (about seven) flat 
and close together, the anterior ones being slightly undercut owing to the 
development of a broad basal ring. The spiral ornamentation is strong 
throughout, with marked reticulation in the earlier whorls; the posterior half of 
the last two whorls is ornamented by thick oblique cost, rather wide apart. 
The sinus-band is submedian, of moderate width and salience, with a raised 
line in the centre (where this feature happens to be preserved). The body-whorl 
is relatively large, subangular at the periphery ; the base is somewhat concave 
midway to the umbilicus, with strong spiral ornament radially decussated. 
Aperture rhomboidal and depressed, the inner lip very oblique. 
Relations and Distribution.—In this species Tawney fancied that he traced a 
resemblance to Pl. Mysis, d’Orbigny, a Middle Lias fossil not hitherto identified in 
England. Indirectly Pl. Dundriensis is connected with the Fasciata-group. 
Rare at Dundry, and only doubtfully identified elsewhere. Not, perhaps, a very 
satisfactory species. 
343. PLEUROTOMARIA DISTINGUENDA, Tawney, 1873. Plate XXXIV, fig. 10, and 
Plate XXXV, fig. 1. 
1873. PLEUROTOMARIA DISTINGUENDA, Tawney. Dundry Gasteropoda, p. 45 (37), 
pl. iii, fig. 2. 
Description : 
Height : ; : : - , £8 mm; 
Basal diameter : : 5 . 20mm. 
Spiral angle . : : ‘ 3 (es 
53 
