PAL/EOSPONDYLUS GUNNI FROM CAITHNESS FLAGSTONES 97 



its relation to other parts the styliform or epihyal process 

 of the skull of the Lamprey. The dichotomisation of the 

 elongated neural spines in the caudal region may also be 

 compared with the same condition in the caudal spinous 

 processes : the so-called fin rays of the Lamprey. 



If I am right in my interpretation of these facts in the 

 structure of Paltzospondylus there seems no escape from the 

 conclusion that the little creature must be classed as a Mar- 

 sipobranch ; and the calcification of its cranium, with the 

 development also of calcified ring-vertebrne in the sheath 

 of the notochord, need be no bar to the acceptation of this 

 view of its affinities, especially if the modern representatives 

 of the group are degenerate forms, as some suppose. It 

 must here be noted that there is no basicranial fontanelle ; 

 so that there could have been no posterior nasal canal, either 

 opening into the pharynx as in Myxinc, or ending in a blind 

 sac as in Petromyzon: 



It is also clear that the hyolingual apparatus, whose 

 absence in the living state can scarcely be conceived, must 

 have been composed of a softer variety of cartilage, uncalci- 

 fied, and therefore incapable of preservation in the rock. It 

 is well known that in the recent Marsipobranchii two varieties 

 of cartilage enter into the formation of the cranio- facial 



o 



apparatus, one of which is considerably harder and more 

 solid than the other ; and a similar condition may have 

 existed in Palceospondylus, the hard cartilage becoming in 

 addition actually calcified. 



Sir J. W. Dawson (6) has suggested an Amphibian affinity 

 for Palceospondylus; but the facts which have come out regard- 

 ing its structure since the work in which he expresses that 

 opinion went to press, render it hardly necessary to discuss 

 that question here, though I have done so in my last paper 

 (7) communicated to the Royal Physical Society. No 

 Amphibian, adult or embryo, with which I am acquainted 

 shows a median cirrated opening, presumably a nose, in the 

 front of the head. 



To sum up the evidence of the Marsipobranch affinity 

 of Palceospondylus we have the following facts : - 



i. The skull is apparently formed of calcified cartilage, 

 and devoid of discrete ossifications. 

 10 D 



