Arthrodires 593 



may, therefore, with propriety isolate it as the representative 

 not only of a peculiar family (Palcsospondylidcs), but of an order 

 or even subclass (Cycliae) of vertebrates which may provisionally 

 (and only provisionally) be retained in the class of Marsipobranchs. 



" The group may be denned as Monorrhines with a continu- 

 ous (?) cranium, a median nasal (?) ring, and a segmented ver- 

 tebral column. 



"The differences between the Hyperoartia and Hypero- 

 treta are very great, and Prof. Lankester did not go much too 

 far when he elevated those groups to class rank. Among 

 the numerous distinctive characters are the great differences 

 in the auditory organs. Perhaps the organs of Pal&ospondylus 

 might be worked out in some specimen and throw light on the 

 subject of affinities. At present even the region of the auditory 

 organs is not exactly known and we are now at a loss to orient 

 the several parts of the cranium. In fact, the question of the 

 relations of Pal&ospondylus is a very open one." 



Views as to the Relationships of Palaeospondylus. Dr. Dean 

 thus summarizes in a convenient and interesting fashion the 

 views of different students of fossil fishes in regard to Palcso- 

 spondylus: 



Huxley. A "baby Coccosteus." 



Traquair, 1890. -- "Certainly not a Placoderm, its resem- 

 blance to a supposed 'baby Coccosteus' being entirely decep- 

 tive. The appearance of the head does remind us in a strange way 

 of the primitive skull of Myxine, a resemblance which is ren- 

 dered still more suggestive by the apparent complete absence 

 of the lower jaw, or of limbs or limb-girdles." 



Traquair, 1893. "It seems, indeed, impossible to refer the 

 organism to any existing vertebrate class, unless it be the Mar- 

 sipobranchs or Cyclostomata. " Does not believe it a larval 

 form, because the possible adult is unknown, and because of 

 the highly differentiated vertebrae. Granting his interpretation 

 of the parts of the fossil, "there seems no escape from the con- 

 clusion that the little creature must be classed as a Marsipo- 

 branch." 



Traquair, 1897. "The question of the affinities of Palao- 

 spondylus is left precisely where it was after I had written my 

 last paper on the subject." 



