474 



CYCLOSTOMATA. 



Palceospondylus gunni. 

 Under this title, Dr. Traquair has recently described a 

 remarkable fossil form from , 



a.c 



the Old Red Sandstone of i.cmui.c 



Caithness. He speaks of it n'i^.v.c 



as a " strange relic of early 

 vertebrate life." 



It is a dainty little creature, 

 somewhat tadpole-like at first 

 sight, usually under an inch in 

 length. The following char- 

 acters point strongly to its 

 affinities with Cyclostomata: — 



(l.) ''The skull is apparently 

 formed of calcified cartilage, and 

 devoid of discrete ossifications." 

 An anterior part is comparable to 

 the trabecular and palatal region of 

 a lamprey's skull ; a posterior part 

 is comparable to the parachordal 

 region and auditory capsules, 



(2.) "There is a median opening 

 or ring, surrounded with cirri, and 

 presumably nasal, in the front of the 

 head" («., Fig. 153).^ 



{3.) " There are neither jaws nor 

 limbs." 



(4.) " The rays which support the 

 caudal fin expansion, apparently 

 springing from the neural and haemal 

 arches, are dichotomised (at least 

 the neural ones), as are the corre- 

 sponding rods in the lamprey." 



Just behind the head lie two small 

 oblong plates {x.. Fig. 153), closely 

 apposed to the commencement of 

 tire vertebral column, one on each 

 side. The notochordal sheath is 

 calcified in the form of ring-shaped 

 or hollow vertebral centra with 

 neural arches. Towards the tail, 

 the arches are produced into slcnd 

 are shorter haemal ones. 



Fig. 153. — Restored skeleton 

 of Pateospondylus. (After 



Traquair.) 



d.c, cirri oi dorsal margin ; /.c, 

 long lateral cirri ; -'.c, cirri of ventral 

 margin ; n., na.'^al ring ; /./., anterior 

 trabecuio-palatine part of cranium ; ^., 

 anterior depression or fenestra ; c, 

 posterior depression or fenestra; a., 

 lobe divided off from anterior part ; 

 /.(X., posterior or parachordal part of 

 cranium ; .r., post occipital plates. 



er neural spines, opposite which 



