PLEUROTOMARIA. A35 
flexuous radii in the base, so characteristic of the species, are lost, and only growth- 
lines remain. Aperture subcircular. 
[ Note as to the figures on Plate XXX VITI.— Figs. 1 a, 1 b, represent two aspects 
of the early adult stage, where strong traces of the actinomphaloid character still 
remain. Fig. 2 represents three aspects of the early stage of one of the more rugose 
forms. Specimens of this size and character are very common in the Concavus-bed at 
Bradford Abbas, though showing much variety amongst themselves. ig. 3 repre- 
sents two aspects of the early stage of a smooth variety, where the staircase-like 
character of the umbilicus is preserved, but the umbilical rays are almost wanting. 
Figs. 4 a, 4b, represent the last stage of Pl. actinomphala-abbas, where the actinom- 
phaloid character is entirely lost, and the shell is smooth alike from age and wear. 
Of these forms, too, there is a very great variety. Most of them exhibit a ten- 
dency to gibbosity in the penultimate whorl; there is also considerable variety in 
the degree of depression, and in some instances the whorls of these old shells are 
so much undercut as to produce quite a different figure. | 
All the above are from the Concavus-bed, Bradford Abbas. In the Murchisonz- 
zone of that locality are specimens which one hardly knows whether to refer to 
Pl. actinomphala, Pl. Aglaia, or Pl. Baugiert. 
376. PreurotomariA Baversrt, d’Orbigny, 1850. Plate XX XIX, figs. 4a, 4b, 4c; 
and var., figs. 5a, 0b, 5c. 
1850. PrEevroromartra BavereRrt, d’ Rieke Prod., i, p. 267. 
1854. — — Terr. Jur., vol. ii, p. 463, pl. 
omelet figs. 2—4. 
Description.—Though not attaining to so large a size, the English specimens 
correspond satisfactorily with those described by d’Orbigny. 
Height (average) ; : . 10mm. 
Basal diameter ; : : . 28mm. 
Shell subdiscoidal, largely umbilicate. The spire is coiled almost in the same 
plane, and is composed of whorls which are subangular and in shallow gradations. 
The whorls are spirally striated, and provided near the upper margin with a furrow, 
the remainder of the space being radially ornamented with about twenty cost 
having tubercular terminations. 
The sinus-band is placed near the outer margin in the furrow, wide, slightly 
sunken, and flanked by raised lines. The body-whorl is subdiscoidal and bluntly 
biangular; the upper carina is formed by the nodular terminations of the 
radial ornaments ; the lower, or peripheral carina, is also strongly nodular and 
