the Sijstematic Poslffon o/'Cniaudlmria. :]20 



of the skull II very eliaractcristic appcaranee in this view. 

 The bones are transparent and the seniieircuhar eanals are 

 very conspicuous through them, rendering it difficult to see 

 the limits o£ the dill'erent bones without very careful 

 examination under a fairly high power of the raicrosoope. 

 The posterior margin of the skull is as broad as the maximum 

 transverse diameter of the frontal region. 



In hiteral view there is nothing very particular to be noted 

 which is not also seen in the dorsai view, except that the 

 sphenotic bone is conspicuous. 



In ventral view (fig. 1, B : tlie nasals omitted) the nasal 

 region only differs from that of Mastacemhelus in the out- 

 lines and proportions of the bones, and in that the antei-ior 

 expansion of the ethmoid is distinctly visible. The lateral 

 expansions of this bone bear a strong ventral ridge, which 

 extends outwards and forwards from the junction of the 

 vomer and the ethmoid. The vomer resembles that of 

 Mastacembelus, and runs into the parasphenoid about the 

 same point. The palatines, however, are much larger and 

 situated further backwards, distinctly behind the orbits. 

 Each forms practically a sector of a circle considerably less 

 than a semicircle, and is joined to the alisphenoid by a long 

 suture. The parasphenoid forms a long narrow ridge with 

 a distinct median longitudinal groove, which gives the bone 

 the appearance of being paired. Behind it a basisphenoid 

 is present in the form of a comparatively large, flat, circular 

 bone, which forms a suture with the palatines, alisphenoids, 

 and basioccipital. The alisphenoids are also large, broad, 

 and flat. They are nearly semicircular in outline. The 

 sphenotic in this view is conspicuous, forming an irregular 

 subquadrate plate, through which the smaller of the two 

 otoliths can be seen by transparency. The pterotic, which 

 is greatly inflated and has an irregular outline, is the largest 

 bone in this pait of the skull. The prootic is also relatively 

 large and considerably inflated. The larger of the two 

 otoliths is conspicuous by transparency through its anterior 

 inner region, extending below the pterotic for a short 

 distance and lying in the sacculus in a prominent capsule 

 C(nnposed of the two bones. The basioccipital is very narrow 

 between the prootics, where it consists of a prominent 

 ridge. This ridge extends forwards to the posterior margin 

 of the basisphenoid, which separates it from the parasphenoid 

 ridge. On either side the bone expands in front into a 

 broad plate of irregular outline in contact with the prootic, 

 pterotic, alisphenoid, and basisphenoid. 



Two otoliths (fig. 2), as we have already indicated, are 

 present on either side of the skull. Both are relativelv 



