510 E. TULLEY NEWTON ON THE REMAINS OF 



PoRTHETTS MANTELLI, n. Sp. 



Unknown fish, Mantell, Geology of Sussex, 1822, p. 241, 

 pi. 42. 



Hypsodon lewesiensis, Agassiz, Poissons Fossiles, 1843, vol. v. 

 pi. 25 b. figs. 1 & 2. 



It is proposed to give the above name to the specimen from the 

 chalk of Lewes, which was first described by Dr. Mantell as an un- 

 known fish, and subsequently included by Agassiz in his species //. 

 lewesiensis, as already mentioned. 



The possession of five teeth in the prsemaxilla shows that this spe- 

 cimen cannot be referred to either P. molossus or P. thaumus, which 

 have only two premaxillary teeth ; and the same character allies it 

 to P. lestrio and P. Mudgei. From the former it differs not only in 

 the shape of the maxilla, but also in the size and number of the 

 teeth — P. lestrio possessing about forty maxillary teeth, while in P. 

 Mantelli there is only evidence of twelve ; and, even if the inter- 

 mediate spaces were naturally occupied by teeth, which is quite 

 possible, yet even then the total number of maxillary teeth could 

 not have exceeded twenty four, and was probably less. These teeth 

 in P. Mantelli are absolutely larger and stouter than those in the 

 P. lestrio figured by Cope, although the specimen itself is not half 

 the size. 



Unfortunately there appears to be no figure of P. Mudgei ; but, 

 judging from the description, it differs from the present species not 

 only in having four of the premaxillary teeth large instead of three, 

 but also in the massiveness of the entire jaw, and in the difference 

 in form of the maxilla ; the maxillary teeth also do not appear to 

 have been so large proportionally as in P. Mantelli. 



The large specimen represented by Agassiz in plate 25 b. fig. 3 of 

 his ' Poissons Fossiles,' vol. v. has all the appearance of being part of 

 a mandible of a large species of Portheus ; but there is no evidence 

 to connect it with the maxilla of P. Mantelli, or with any other 

 species. 



There is in the British Museum (no. 39063) a large Portlieus 

 maxilla from the Chalk (formerly in Dr. Bowerbank's collection), 

 which has large teeth, in some respects like those of P. Mantelli ; 

 but as both ends are imperfect, a close comparison cannot be made. 

 The straightness of the dentary margin, however, seems to point 

 to its being a distinct species. 



A fragment of a very large Portheus jaw, probably a lower one, 

 from the Chalk of Warminster, also preserved in the British 

 Museum (no. 46389), must have belonged to a species as large 

 as Cope's P. lestrio. The teeth are much broken ; but portions 

 of five are preserved : they are oval in section, the central largest 

 one having a diameter of about T 7 ^- of an inch, and when per- 

 fect must have measured fully 4 inches in length, including the 

 fans:. 



