Dr. R. H. Traquair on the Genus Dipterus. 11 



which may be explicable by a reference to the condition of 

 the tail in Protopterus and at least some specimens of Cera- 

 todus^. Here the notochord stops short before reaching the 

 extremity of the tail, and the bases of the vertebral arches, 

 which have been proportionately increasing in depth, meet 

 each other from above and fuse together, each neural one with 

 the corresponding hjemal opposite, so as to produce, as Dr. 

 Giinther observes, " a district vertical segmentation,^^ some 

 amount of ossification in which might, in Dijjterus, have pro- 

 duced the appearance in question. 



The heterocercy of Dipterus, and the differentiation from 

 the median fin-system of two dorsals and one anal, distinct 

 from the caudal, are points which can only be looked upon as 

 of " family " importance. Some difference from Ceratodus 

 is observable in the structure and arrangement of the median- 

 fin rays, but not to the extent that Dr. Giinther has stated. 

 These rays are closely set; but tracing them towards their 

 origins they are seen to converge into small fasciculi, each of 

 which apparently results from the division of an original ray; 

 the rays are also unarticulated up to a certain point, from 

 which they become closely jointed to their terminations. It 

 is quite clear that the unarticulated proximal portions of these 

 rays are what Pander has described as interspinous bones 

 (" Flossentrager ") ; and, following this interpretation. Dr. 

 Giinther has indicated as an important point of distinction 

 between Ceratodus and Dipterus that the latter has its " inter- 

 neural and interha^mal spines branched at their distal end, 

 to which the dermal rays are joined." The real fin-ray, how- 

 ever, includes both what is here considered as " I'a^y" and as 

 " interneural " or " interh^mal spines ;" and its proximal 

 extremity in reality overlaps, as might tie expected, the real 

 series of interspinous elements, which, however, are seldom 

 seen, owing to the scaly covering of the body. 



As the result of the observations briefly recorded above, I 

 feel myself compelled to differ from Prof, Huxley in his 

 opinion that Dipterus is much more similar to Polypterus and 

 Amia than to the living Dipnoi in other respects than its 

 dentition and the form of its fins — as well as from Mr. Miall, 

 in his statement that " it is not easy to say whether the re- 

 semblances or the differences between the Dipnoi and the 

 Ctenododipterini are of greater weight." Agreeing, however, 

 with the last-named author, that " the presence or absence of 

 gidar plates is hardly of ordinal value," the correspondence 

 between Dip)ter^is and Ceratodus in all points of real ordinal 



* fiimtber, op. cit. p. o27, pi. xxx. fig. 3. 



