52 FAUNA OF THE CORNBRASH. 



whorl is 40 mm. The thickness is comparatively small, though immeasurable. 

 The surface slopes gently towards the umbilicus, but turns over rapidly to the 

 narrow periphery. The surface is ornamented on the umbilical half by about 

 ten ribs per quadrant. These are rather narrow and have a curvature some- 

 what convex to the aperture ; about half-way out they form the base of three 

 times as many peripheral ribs, with the convexity reversed. The grouping of 

 the inner and outer portions is irregular — the latter pass over the periphery 

 unaltered. The whole group has a scourge-like appearance. No further details 

 are observable. The specimen is in the collection of the author and comes 

 from the part of the series which lies above the rubble bed in Bast Fleet, near 

 Weymouth. 



Description. — So far as it can be tested this appears to agree in every way, 

 except in the sigmoidal bend of the ornament, with the shell figured by Quenstedt, 

 loc. cit., as "Am. cf. arbustigerus, D'Orb." D'Orbigny's Great Oolite species, 

 however, is thicker and narrower whorled, with different ornament in detail. 

 Quenstedt's, on the other hand, besides the agreement in the measurable details, is 

 said to have " roughly trifurcate ribs," which, however, are rather indistinct. 

 Though it " has a certain relation to its companion A. macroceplialus, it cannot 

 be denied that its rate of increase in thickness is somewhat too slow." 



Distribution. — Besides the above I have seen two smaller fragments, one 

 from Radipole and another from Sutton Benger, which, by the small slope of 

 the umbilical half and the strength of the inner ribs, may possibly belong to 

 the same species as this. 



Specimens unnamed. 



Perisphinctes, sp. 1. Plate V, fig. 4. 



Description. — A specimen obtained from the rubbly beds of South Cerny is 

 certainly distinct from any of the above. It consists of a quadrant of the 

 outer whorl and the impression on the matrix of the inner whorls, but it is, 

 unfortunately, not well enough preserved to yield definite characters, except 

 the shape of the section as shown in PI. V, fig. 4. This is seen to be slightly 

 transverse (36 — 33) at the spot chosen (from knob to knob), and to overlap but 

 slightly the previous whorls. On the surface of the quadrant, near but not at 

 the umbilical edge, there are signs of six radial knobs, beyond which are about 

 twenty peripheral riblets in the same space. These are not actually seen passing 

 from side to side, but the surface is here worn away. On the inner whorls the 

 knobs seem to be closer together, as if they were only elevations of ordinary 

 inner ribs. 



