346 DR. BASIIFOllD DEAN ON PATiiEOSPONDYLUS GUNNI. [Apr. 19, 



absolutely unknown in tlie entire craniote phylum, — a terminal 

 monorhinal ring bearing barbel-like structures. This would entail 

 the development of a new theory of the vertebrate bead, the cirrho- 

 rhinal, as opposed to the cirrhosfomial theory of Pollard. That this 

 departure from our old-fashioned ideas of marsipobranch morphology 



Characters of Pala'osponclyhis with reference to Marsipobrancbs. 



Evidence 



Oral cirri 



Jaw part8 



Cranium 



Vertebral 

 column. 



Paired fins. 



Caudal fin 



Favourable 



Suggest somewhat the 

 barbels of tbe naso- 

 moutb region of myxi- 

 noid 



UnfavourMe 



Unknown 



Essentially marsipo- 

 braiichian, especially 

 its dichotomous rays. 



Resemble even as nnicb in arrange- 

 ment and greater number the buccal 

 cirri of Amphioxns. Dr. Traquair's 

 evidence of eirrorbiny (protocbor- 

 date?). On tbe other hand, simi- 

 lar niouth-surrouuding tentacles 

 evolved independently in many 

 groups of fishes — siluroids, sharks, 

 forms like Pogovias, Hemitriptenis. 

 A possibility, further, that the 

 " cirri " may turn out to be reuinant.s 

 of i-ranial or facial structures of an 

 entirely different nature. 



Unknown. Possibility that the ven- 

 tral rim of tbe "nasal ring" may 

 prove to be tbe remains of Meckelian 

 cartilage. ( Vide Ann. .Scot. Nat. Hist. 

 1804, pi. iii. fig.s. 1, 2). 



Utterly non-marsipobranchian. Mas- 

 sive cranium, over twice as large 

 )3roportionately as in tbe lamprey. 

 Huge auditory (?) capsules. 



Utterly non-marsipobrancbian. High- 

 ly evolved. Massive centra, promi- 

 nent neural arches. 



Fatal evidence against marsipo- 

 branch atfinities, if the raj'-sbaped 

 markings are admitted to be the 

 basalia of paired fins. Their pre- 

 sence is alone sufficient, ceteris pari- 

 bus, to cause Palaospondylvs to be 

 removed from its provisional posi- 

 tion among tbe Oyclostomes. Also 

 the " post-occipital plates " possibly 

 represent a pectoral arch. 



Its condition also common, as diphy- 

 cercy (and gephyrocercy), in other 

 groups of fishes — sharks,.lung-fishe8, 

 teleostomes. 



was, however, actually intended becomes evident from his remarks 

 on my earlier paper. And I sincerely apologize for having mis- 

 understood his meaning. For now it appears that he interprets 

 the ring and its cirri as ''cranial'' structures, and they must 

 therefore be entirely unlike the niyxinoid ring, which is clearly 



