242 Dr. R. H. Traquair — On Cycloptychius carhonarius. 



No. 1. 

 inches, lines. 

 4 1 

 10 



No. 2. 

 inches, lines. 



10 



No. 3. 

 inches, lines. 

 3 10 

 10 



1 9 



I 9 



1 3 



2 6 



2 4 



2 



3 5 

 8 



3 



7 



2 10 

 10 







11 



7 



absolutely perfect tail in the suite of specimens (PI. XII. Fig. 2) 

 unfortunately wants the head and fore-part of the body. 



No. 4. 

 inches, lines. 

 Entire length (approximate) , 



Length of head 



From tip of snout to opposite origin 



of ventral fin 19 19 13 1 



From tip of snout to opposite origin 



of dorsal fin. 

 From tip of snout to opposite origin 



of caudal fin.... 

 Depth at shoulders. 



Nos. 3 and 4: are proportionately shorter and deeper ; and, while 

 Nos. 1 and 2 agree in their measurements as far as the dorsal fin, the 

 distance between that and the caudal is less in No. 2 than in No. 1. 

 Again, in a fifth specimen, that represented in PI. XII. Pig. 2, the 

 distance between the dorsal and anal fins and the cavidal is propor- 

 tionately greater than in either of the two last mentioned, as is also 

 the case in yet another example of the slender variety. Neverthe- 

 less, I cannot think that any specific distinctions are indicated by 

 these differences in the measurements ; the specimens agree too well 

 in other essential points. We must, in fact, besides individual varia- 

 bility, take into account changes occurring after death, and in the 

 course of entombment and mineralization, by which more or less 

 distortion and change of the original form and proportions must 

 have been produced. The bodies of the shorter forms. No. 3 and 

 No. 4, show a peculiar corrugated and almost crumpled aspect, seen 

 also in the part between the anal and caudal fins in No. 1 and No. 2, 

 in which that region is shorter than in the two still more elongated 

 forms alluded to. The normal shape of the fish, when alive, would, 

 I think, on the whole correspond with that of the more slender 

 examples, the head occujoying about 3th of the total length, while 

 the ventrals would be situated at rather less than -f-ths, and the 

 beginning of the dorsal and anal fins at less than |-ths from the tip 

 of the snout. 



Head. — The osteology of the head, so far as can be made out, 

 closely corresponds in general plan with that in Palceoniscus. In 

 none of the specimens can a clear view be obtained of the individual 

 form and boundaries of the bones of the cranial roof ; their external 

 surfaces seem however to have been finely tuberculated, the tubercles 

 sometimes being confluent into short ridges. There is distinct 

 evidence of extensive ossification of the base and side walls of the 

 cranium, but here again it is impossible to make out the individual 

 bones. The ethmoidal region is prominent, and forms a bluntly- 

 pointed projecting muzzle. The bones of the face are more distinct, 

 and many of them quite determinable. The liyomandihular (Fig. 4, 

 and Fig. 3 hm.), partly seen in front of the operculum in most of the 

 heads, and quite isolated in one specimen, is a somewhat long-shaped 

 bone, which descends obliquely downwards and backwards towards 

 the articulation of the lower jaw, thus carrying the gape very far 



