256 Messrs. Hancock and Atthey ooi 



Codacanthus lepturus, Agassiz. 



We have long had in our possession certain mandibuliform 

 bones from the Newsham shale, evidently piscine, though we 

 could not make out to what species or even to what genus 

 they belonged ; and it was not till some short time ago, 

 when we fortunately obtained a crushed head of Coelacanthus, 

 that the enigma was solved. This specimen exhibits our 

 supposed mandible in connexion with the rather strangely 

 formed bone figured and described in the ' Memoirs of the 

 Geological Survey,' Decade 12, by Professor Huxley, as the 

 mandible, and so placed in relationship to it that it became at 

 once evident that the mandible of Huxley is merely the arti- 

 cular piece, and our supposed mandible the dentary bone. 



The articular piece is well represented in the memoir re- 

 ferred to. We have three or four isolated specimens of it in 

 a good state of preservation ; also one or two others in con- 

 nexion with the bones of the head and united to the dentary 

 bone. The articular piece (PL XVII. fig. 4, a) is long and 

 narrow, with a large arched lobe rising from the upper margin 

 and situated a little nearer to the proximal than the distal ex- 

 tremity ; the proximal extremity is obtusely pointed, and the 

 upper border is occupied by a narrow longitudinal channel 

 (the glenoid surface, ?>), which widens a little backwards and is 

 twisted or inclined to the external surface ; tlie borders of the 

 . distal extremity are nearly parallel, and in front it thins out 

 and is diagonally truncated forwards and upwards. Our 

 largest specimen is about two and a half inches long, and at 

 the widest part measures five eighths of an inch across. 



The dentary bone (fig. 4 c) is as peculiar in form as the 

 articular piece : it is narrow and semicylindrical in front, the 

 outer surface being convex, the inner channelled or concave ; 

 the posterior portion, more than half the entire length, widens 

 backwards, and has the upper and lower borders somewhat 

 thickened; the proximal extremity thins out, is truncated 

 diagonally downwards and backwards, and has the lower 

 border, which is the longer, produced into a point. The whole 

 bone is strongly arched, the lower margin being regularly 

 convex ; the symphysial surface is not distinguishable, and 

 was probably formed chiefly by the cartilage that undoubtedly 

 occupied the groove or channel of the inner surface. 



The teeth \d) are placed on the upper border of the ex- 

 panded portion, and extend in a close series of from six to 

 eight from the posterior extremity almost to the junction of 

 the border with the anterior semicylindrical portion of the 

 bone : the dentary area is thus very limited. The teeth are 



