STROPHODUS MAGNUS. 29 



ridge. The posterior half of the spine has a number of tooth-like projections, 

 curved in the proximal direction and polished on the distal side. They seem to 

 stand irregularly, but actually occur in a series of oblique pairs, with a zig-zag 

 median line running between the members of each pair. This species differs 

 from Ast. wastensis, from the Cornbrash of Boulogne, in that the latter has no 

 tubercles throughout distinct (see Sauvage, ' Bull. Soc. Geol. France,' ser. 3, 

 vol. viii, p. 454, pi. xiv, fig. 5). 



Distribution. — This specimen is in the British Museum (no. 47131), and was 

 obtained from the Sharp collection, being recorded by Sharp as Asteracanthus 

 verrucosus and stated to be obtained from the Cornbrash at St. Botolph's Bridge, 

 Peterborough, probably from a railway cutting now grassed over. No such spines 

 are known from the Great Oolite, and the type comes from the clay overlying the 

 Cornbrash at Castle Mills east of Bedford. 



Genus STROPHODUS, Agassiz. 



This genus was founded for teeth only (' Poissons Fossiles,' vol. iii, 1838), 

 some of which were separated by Sauvage as Curtodus (' Cat. Poiss. Foss. 

 Boulonnais,' p. 53, 1867). These names are regarded only as temporary by A. S. 

 Woodward, the teeth definitely found associated with Asteracanthus appearing under 

 that name only. The teeth are said by Agassiz to be " elongated, more or less 

 reticulated and truncated at the ends, showing a torsion in the direction of the 

 long diameter, more or less elevated in the centre or at one end, reticulated on the 

 surface, but without any elevated crest in any particular direction, root flat 

 and broad." In the specimen figured by Owen, however (' Geol. Mag.,' 1869, 

 vol. vi, pi. vii), it is seen that Strophodonts are of different shapes in different 

 parts of the mouth. The innermost row (1) is smaller and more elevated 

 than the second (2), which is larger and more irregular in shape, while the 

 other two outermost (3, 4) are the largest, longest, and flattest. These are 

 succeeded by smaller series of teeth running transversely. There may be also 

 a symphysial set of teeth of quite a distinct shape in one of the jaws. The 

 ornament of the enamel, however, seems to be of the same general type 

 throughout. Thus, the genus Curtodus, founded on the difference of shape — 

 inflated instead of twisted longitudinally — loses its significance. 



Strophodus magnus, Agassiz. 



1838. Strophodus magnus, Agassiz, Poiss. Foss., vol. iii, p. IlVI, pi. xviii, figs. 11 — 15. 

 1889. — — A. S. W Lward, Cat. Foss. Fishes, B. M., p. 315. 



