104 MESSKS. HANCOCK AND ATTHEY ON 



simple range appear to garnish the circumference of the mouth.* 

 The species in which the teeth have been determined is A. j^usil- 

 liis ; and of this the same author writes that the mouth is " gar- 

 nie de tres-petites dents qui, meme sous une tres-forte loupe, ne 

 paraissent que comme des petits points noirs."f This is so 

 definite that it is impossible to doubt its accuracy; we are there- 

 fore forced to the conclusion that in this genus, as at present 

 understood, there are two very distinct kinds of dentition, so dis- 

 tinct, indeed, that it seems necessary to establish a new genus 

 for the reception of those species, which, like A. Warcli, may 

 have large triangular teeth, similar to those alluded to. We 

 therefore propose the generic appellation of Acanthodojms for 

 those Acanthodei with this peculiar dentition. 



The remains in our possession of such fishes are divisible into 

 two species by the characters of the spines, scales, and teeth. 

 One of these is very much larger than the other. It is the 

 smaller of the two that appears to be identical with A. Wardi. 

 The larger species is probably the same as that of which Sir P. 

 Egerton had obtained the head and anterior parts, and which 

 is supposed by him to "have measured two feet six inches in 

 length."]: A pectoral spine of this is stated to have been 3| 

 inches long. 



The mandibular ramus of A. Wardi (Plate II., fig. 6) is about 

 Ih inches long and |^th of an inch wide at the broadest part, 

 which is near the proximal extremity, whence it tapers gradually 

 to the distal end, which is rounded ; the proximal end turns 

 upwards, and presents a well-defined concave articular surface. 

 The dentigerous bone is very thin, and its walls are usually 

 pressed close together ; the outer wall is irregularly striated 

 longitudinally, the inner wall is smooth ; the lower margin is 

 strengthened by a stout styliform process, c, which is very liable 

 to detach itself, when it assumes the appearance of a cylindrical 

 spine graduating to a point in front ; it is united behind to the 



* " Poissons Fossiles " du Vieux Grfes Rouge, premiere livraison, p. 39. 



t Ibid, p. 36. 



X ■' Quarterl> Journal Geological Societj-,'' Vol. XXII., p. 470. 



