"The group may be defined as Monorrhines with a continuous (?) cranium, a median nasal (?) ring, and a segmented vertebral column.
"The differences between the Hyperoartia and Hyperotreta 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 Palæospondylus 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 Palæospondylus is a very open one."
Views as to the Relationships of Palæospondylus.—Dr. Dean thus summarizes in a convenient and interesting fashion the views of different students of fossil fishes in regard to Palæospondylus:
Huxley.—A "baby Coccosteus."
Traquair, 1890.—"Certainly not a Placoderm, its resemblance to a supposed 'baby Coccosteus' being entirely deceptive. The appearance of the head does remind us in a strange way of the primitive skull of Myxine, a resemblance which is rendered 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 Marsipobranchs or Cyclostomata." Does not believe it a larval form, because the possible adult is unknown, and because of the highly differentiated vertebræ. Granting his interpretation of the parts of the fossil, "there seems no escape from the conclusion that the little creature must be classed as a Marsipobranch."
Traquair, 1897.—"The question of the affinities of Palæospondylus is left precisely where it was after I had written my last paper on the subject."
Smith Woodward, 1892.—"It seems to possess an unpaired nose, lip cartilages in place of functional jaws, and no paired limbs; thus agreeing precisely with the lampreys and hagfishes, of which the fossil representatives have long been sought. It is extremely probable, therefore, that Palæospondylus belongs to this interesting category."
Dawson, 1893.—Palæospondylus suggests "the smaller snake-like Batrachians of the Carboniferous and Permian; and I should not be surprised if it should come to be regarded as either a forerunner of the Batrachians or as a primitive tadpole."