and their RdationsM]) to Ceratodus Forsteri. 193 



the occipitals, witli a portion of the parietals and the lateral 

 bones, all lying in their natural positions and united into one 

 mass, the component parts being distinguished by well-marked 

 sutures ; and the whole so closely resemble the same bones 

 in Dipterus that they might be taken to belong to a gigantic 

 specimen of that genus. This fragmentary skull is eight and 

 a half inches across the occiput. 



The posterior portions of three other skulls have likewise 

 been found : these belong to G. ohliquus \ they are nearly 

 perfect, and one of them displays the bones up to and including 

 the parietals. The surface is in excellent order, and is more 

 coarsely pitted or punctate than in the former species, and 

 exhibits throughout a semigloss ; the sutures are quite di- 

 stinct. The bones vary in form only specifically from those of 

 C. tuberculatus : the occipital is the most characteristic, the 

 frontal margin of which is dee2:>ly concave, while in the latter 

 it projects and has a wedge-shaped process in the centre. 

 This beautiful specimen measures seven inches across. The 

 two other examples agree in all their characters with the 

 above ; but some of the lateral bones of one side are wanting. 

 As in Dipterus^ the component bones in Ctenodus are com- 

 paratively small, vary little in size, are many-sided, and fit 

 together like a mosaic pavement or like the pieces of a Chinese 

 puzzle. And that the anterior bones of the skull are of the 

 same character, we have ample evidence in numerous separate 

 bones that have occurred at Newsham, which, though differ- 

 ing in form from those composing the fragmentary skulls, un- 

 doubtedly belong to Ctenodus, 



Another specimen, showing half of the bones of the occi- 

 pital region, including the parietals, has occurred. This may 

 perhaps belong to C. cristatus ; at all events it is a portion of 

 the skull of one of the larger species, for it is of considerable 

 size. And that it cannot belong to either of the above two 

 species is proved by the form of the median occipital, which 

 differs greatly from that of both. It is strongly pointed in 

 front, and the lateral posterior margins are remarkably sinuous; 

 the surface-structure, too, is different. 



The bones that are determinable in the above fragmentary 

 skulls are the median and external occipitals, the anterior oc- 

 cipitals, the parietals, and the lateral or " skin bones" according 

 to Pander, of which only the three posterior are present. The 

 arrangement of these bones is precisely similar to that given 

 in Pander's restored figure of the cranial shield of Dipterus 

 (tab. 3. fig. 1), the principal difference being that they vary 

 even less in size than those in the figure ; the median occipital 

 in C. tuherculatus is scarcely, if at all, larger than the other 



Ann. & Mag. N. Hist. Ser. 4. Vol.\n. 14 



