484 A. S. Woodicard — Canadian Devonian Fishes. 



border. The lateral occipital {I. occ), marginal (m.), preorbital 

 (p. o.), postorbital (j^t. o.), and pineal (p.) plates are imperfect and 

 do not require special note; "while the central plates (c.) form a 

 relatively small and not quite symmetrical pair. The sensory canals 

 of each side are distinctly united in the usual manner by a transverse 

 commissure across the central plates ; and it may be added that the 

 white mark on the lateral occipital of the right side in the drawing 

 is an indication merely of a fracture. 



Coccostens is already well known to occur in the typical Upper 

 Old lied Sandstone ; and it is interesting to note that in Russia, as in 

 Canada, the genus is found in association with species of Bothnole2ns. 



III. On the Supposed Jaws of Boihriolepis. 



In the new collection the British Museum acquires many fine 

 examples of Bothriolepis, some displaying features not hitherto 

 observed ; but the most striking specimens are two exhibiting the 

 supposed jaws. 



It has long been known that a pair of loose, narrow plates occurs 

 on the inferior face of the head in the Asterolepidee. These plates 

 were interpreted by Pander,^ as the two rami of the lower jaw; 

 and they are placed by Traquair- in juxtaposition with the anterior 

 border of the ventral bod3'^-shield as " mental plates," of uncertain, 

 though possibly mandibular function. By Whiteaves,^ however, 

 the pair of elements in Bothriolepis is represented as immediately 

 adjoining the front margin of the dorsal shield, while the space for 

 the mouth occurs behind. It is the latter interpretation that now 

 proves to be correct, and a diagrammatic sketch of the parts in the 

 critical specimen (No. P. 6761) is given in the accompanying Wood- 

 cut, Fig. 2. 



Fig. 2. — Supposed jaw-plates of Bothriolepis canadensis. 



This drawing, it will be observed, agrees well with that of the 

 corresponding parts already given by Whiteaves (loc. cit. pi. vii.) 

 merely adding some important details. In all the specimens of 

 Bothriolepis canadensis in which the present writer has been able 

 to examine the plates in question, they occur in close apposition to 

 the anterior margin of the head-shield as here shown; and it is 

 noteworthy that there are traces of an excavation of the short 

 externo-lateral margin of each of these plates, as if providing space 



^ C. H. Pander, "Die Placodernien des Devonischen Systems," p. 49 (18-57). 

 : - R. H. Traquair, " On the Structure and Classiticatiou of the Asterolepidse," 

 Ann. Mas- Nat. Hist. [6] vol. ii. p. 488, pi. xvii. fig. 2 (1888), 

 ■ * Trans. Eoy. Soc. Canada, vol. iv. sect. iv. pi. vii. (1886). 



