212 



THE GEOLOGIST. 



in the Mantell collection. The teeth have not been found in any 

 strata more recent than the Wealden. As far, therefore, as the 

 evidence goes, it seems much more likely to be of an age anterior to 

 the Cretaceous system." This, then, is at most only doubtfully a Cre- 

 taceous species ; and the only other instance of which we have any 

 published figure or description is the Hybodus sulcatus referred to by 

 Sir Philip, and recorded in Morris's " Catalogue," on the authority 

 of Agassiz (vol. iii. p. 44, t. 106, fig. 15, 16), as from the chalk of 

 Lewes in Sussex. All Agassiz says is, " M. Mantell possesses two 

 fragments of rays of a Hybodus found in the chalk of Lewes, but 

 which are in a bad state of preservation. One recognizes, however, on 

 the surface the furrows and the longitudinal ridges, characteristic of 

 Hybodus, which present this particularity, that they are very straight 

 (droites) and very uniform. At the posterior edge one distinguishes 

 a well-marked longitudinal ridge (fig. 16a) , which constitutes a spe- 

 cific character sufficiently defined to permit the founding of a species 

 upon such imperfect pieces. I have not seen any teeth on the pos- 

 terior sides ; I doubt not, however, that such existed, but they have 

 probably been broken, which does not appear astonishing in frag- 

 ments so damaged." These two fragments, little more than an inch 

 each in length, are now in the British Museum ; and a careful inspec- 

 tion has convinced me that grains of Wealden grit still adhere 

 to them, and, therefore, that they can no longer be regarded as even 

 Cretaceous still less as Chalk specimens. No Chalk fossils were ever 

 seen of such a peculiar nature as the substance of which they are 

 composed. There remain, then, to retain Hybodus as a Cretaceous 

 species, only those relics, whatever they are, which Professor Morris 

 has recorded as " species : Chalk, Northfleet (Collection "Wetherell) ; 

 Norfolk (Rose)," and which have never yet been figured nor described.* 

 Very great interest, therefore, attached itself at once to a small but 

 very fine and delicately-preserved jaw, with numerous teeth, to which 

 my attention was drawn, in the National Collection (No. 36908). 

 It is from the Lower Chalk of Dover. The extreme length of the 

 right ramus of the lower jaw is 2\ inches ; its vertical depth at the 

 middle and deepest part, f of an inch ; and the depth of the upper 

 and lower jaws together, 1^ inch. There are twenty-five teeth in all, 

 fully visible, and fragments may be detected of one or two more. 



* Mr. Hose informs me that the reference in Morris's Catalogue is to a specimen in 

 his collection identical with the ickthyodorulite figured in Dixon's Geology of Sussex,' 

 tab. xxxii. fig. 7, which, however, is not Hybodus. Mr. Rose's specimen is from the 

 Lower Hard Chalk of Whittington, near Stoke Ferry, West Norfolk. What the speci- 

 mens in Mr. Wetherell's collection are we do not know. — S. J. M. 



