PYCNODONT TEETH OF UNCERTAIN GHNERIC POSITION. 167 
Specific Characters.—A large species known only by the splenial dentition. 
Teeth of principal series on the splenial bone smooth or feebly crimped round the 
margin, somewhat less than three times as broad as long, about equalling in width 
the two outer series, which are nearly similar in size, irregular in form, slightly 
broader than long, and having a deep coronal pit with rugose or crimped margin. 
Horizon and Locality.—Zone of Holaster subglobosus : Halling, Kent. 
Pycnopont TrrerH or UNcEertTAIN Generic Poston. 
1. Gyrodus (2) cretaceus, Agassiz. Plate XXXV, figs. 5—7. 
1833-39. Spherodus mammillaris, L. Agassiz, Poiss. Foss., vol. i, pt. i, p. 15 (in part), pl. Ixxin, 
figs. 1, 2. 
1839-44. Gyrodus cretaceus, L. Agassiz, ibid , vol. ii, pt. 11, p. 253, pl. lxixa, fig. 13. 
1840. Gyrodus cretaceus, R. Owen, Odontography, p. 72. 
1844. Gyrodus mammillaris, L. Agassiz, op. cit., vol. 1, pt. 11. p. 236. 
1844. Pycnodus marginalis, L. Agassiz, op. cit., vol. 11, pt. u, p. 199. 
1850. Gyrodus cretaceus, F. Dixon, Geol. Sussex, p. 370, pl. xxx, fig. 15. 
1850. Gyrodus conicus, F. Dixon, ibid., p. 370, pl. xxxii, fig. 8. 
1888. Gyrodus cretaceus, A.S. Woodward, Proc. Geol. Assoc., vol. x, p. 308. 
1895. Gyrodus (2) cretaceus, A. S. Woodward, Catal. Foss. Fishes B. M., pt. 1, p. 245. 
T'ype.—Portion of vomerine dentition. 
Specific Characters—Dental crowns much elevated, obtusely acuminate, 
and coarsely rugose; those of the median and outer paired series on the vomer 
usually longer than broad, about equal in size; teeth of inner paired series on 
this bone relatively small and multiphed in the adult. 
Description of Specimens.—The type specimen, said to have been in the 
Mantell Collection, cannot be found; and the portion of splenial dentition 
named Gyrodus conicus by Dixon is not traceable. The isolated teeth named 
Spherodus mammillaris and Pycnodus marginalis have also been lost. Good 
examples of the vomerine dentition, however, are known, and there is one 
fragment apparently of the splemial dentition. 
The best specimen of vomerine teeth, already figured by Dixon, is shown 
again in Pl. XXXV, fig. 5. All the teeth are more or less conical and rugose, 
often with a flattened rim or cingulum; and some of the smaller teeth are 
mammuilliform, their median boss being rounded and sharply defined. When they 
are worn their internal cavity is soon exposed at the apex, and the abraded 
surface of the dentine is coarsely punctate. Their arrangement is remarkably 
irregular, and the inner paired series is represented on each side by more than 
one row of teeth. The teeth of the median series are not larger than those of 
