Contribution to Knowledge of Paleeospondylus Gunni. 313 
specimens, one of which shows the structure of the tail-fin in 
a much more perfect manner than has ever been previously 
observed. 
It will be remembered that in my last communication I 
described the cranium of Palwospondylus as consisting of two 
parts—an anterior, comparable to the trabecular and palatal 
part of the lamprey’s skull; and a posterior, in like manner 
comparable to the parachordal part and anditory capsules. 
No differentiated bones could be seen in this cranium, which 
apparently consisted of calcified cartilage. No trace of jaws 
or of hyoid apparatus could be seen in any of the numerous 
specimens examined; but the anterior margin of the head, 
bearing four pointed cirri, was compared by me to the upper 
margin of a suctorial mouth. If the creature was of Marsipo- 
branch affinity, and many points in its configuration were 
highly suggestive of that idea, evidence as to the condition 
of the nasal organ would have been of the utmost importance; 
but no evidence on this point was forthcoming. 
What the new facts are will now be seen. 
Among my new specimens, the most remarkable head is 
that represented in Pl. 1X., Fig. 1, magnified five diameters. 
It will here be seen that the part which I represented in my 
former figures as the anterior margin of the head with four 
cirri, two outer and longer, two inner and shorter, and which 
I compared to the upper margin of a suctorial mouth, is in 
reality the lower or ventral lip of a median depression or 
opening, which is fringed with cirri all round. This opening 
appears transversely oval, though it may have been so com- 
pressed from an originally round shape. Along its ventral 
margin are seen four cirri (v.c.), while the upper margin 
shows five (d.c.), one of which is median. But there are in 
addition two other and longer cirri (/.c.), which seem to arise 
within the rim of the opening on each side, not from its 
margin as the others do; and these are evidently the two 
longer and external cirri shown in my previous figures, as 
well as in the figures given by Smith Woodward and Dawson 
(4, fig. 1; 6, fig., p. 285). 
Fig. 2 represents a head in a similar state of preservation, 
but the inner cirri of the ventral margin of the opening are 
