Description of Paleospondylus Gunni. Y3 
place on the ventral aspect of the axis, but here they are 
shorter, and the fin-like expansion consequently is not so 
deep. No interspinous elements and no fin-rays can be 
detected, yet Palwospondylus may be said to have a proto- 
cercal tail, and it is also interesting to observe that here 
the upper or dorsal fin-expansion is deeper than the lower 
or ventral one. Mr Woodward does not emphasise this in 
his figure, and he has also represented the neural and hemal 
spines as much less oblique than they really are. He has 
also represented the vertebral centra all the way along as 
separated by intervals from each other, a condition which, 
according to my specimens, only occurs with the vertebra 
immediately behind the head, 
SUMMARY. 
I have at present no further details regarding the structure 
of Palwospondylus, though there is every ground for hope that 
still better specimens may turn up in the locality in course 
of time. Meanwhile, what is already known may be 
summarised as follows :— 
1. The cranium is of a simple structure, and no distinctly 
differentiated bones can be detected in its composition. It 
is seen only from the ventral surface, and consists of two 
parts—an anterior, comparable to the trabecular and palatal 
part of the lamprey’s skull; and a posterior, also comparable 
to the parachordal part and auditory capsules. Evidence as 
to the condition of the nasal organ is deficient. The anterior 
margin shows several pointed processes or cirrhi. No trace 
of jaws have ever been detected in any of the numerous 
specimens which have been examined. 
2. Immediately behind the head are two small, oblong, 
plate-like bodies, which in their natural position lie closely 
apposed to the commencement of the vertebral column, one on 
each side. Their morphological signification is quite obscure. 
3. The notochordal sheath is calcified in the form of ring- 
shaped or hollow vertebral centra. These are furnished with 
neural arches, which, towards the caudal ‘extremity, become 
produced into slender neural spines, while at the same place 
