2) =e ee 
< om 
Mr. T. Stock on the Genus Tristychius. 187 
tooth (Pl. VII. fig. 18) the middle cusp is much lower than in 
the others; and as it lies with its convex aspect uppermost, 
deeply grooved and prominently ridged, the lateral cusps on 
one side hardly at all differentiated from the rest of the free area, 
the resemblance to Ctenoptychius pectinatus is striking. In 
other places, particularly in one place (it requires close obser- 
vation to detect it), the appearances are interpretable as those 
of a series of fan-shaped, ridged, and denticulated bodies, 
resembling the smaller forms of Ctenoptychius sectinatus. 
It is just here, however, in these crucial cases, where obser- 
vation is most difficult. A little confirmatory evidence may 
be gleaned from the observations and figures of Giebel*, pre- 
viously discussed. His Styracodus acutus | reminds one of 
Ctenoptychius, and is accompanied by a spine which appears 
to resemble that of Zristychius. 
At Burgh Lee, where the Carboniferous beds have been 
searched for fossils perhaps more thoroughly than in any 
other locality in this district, Zristychius is one of the com- 
monest spines, as Ctenoptychius pectinatus is one of the 
commonest fossils; yet, strange to say, the teeth (of which a 
good view has been obtained in the specimens that I have 
described) have never, so far as I know, been detected in that 
locality. I have obtained Zristychius spines and Ctenopty- 
chius pectinatus associated in the fish-bed at Abden, near 
Kinghorn, Fife, but not the undoubted teeth of Tristychius. 
On the Wardie horizon, again, I have obtaimed the teeth and 
spines of Ziristychius, but not a single detached undoubted 
Ctenoptychius. In the English Coal-measures Ctenoptychius 
pectinatus is common ; but neither spines of Zristychvus nor 
undoubted Zizsiychius teeth have been, so far as I know, dis- 
covered{. It will thus be seen that the evidence from associ- 
ation or the lack of it is exceedingly conflicting and of dubious 
value, whether for the affirmative side or the negative. 
On the whole, whilst believing that the two forms of teeth 
will be found to belong to the same fish, I do not yet 
consider it placed beyond question, and some reserve must 
be exercised before deducing much from it. 
Summary.—TVhe preceding descriptions indicate a shark of 
small size. ‘The buccal opening seems to have been of con- 
siderable relative dimensions. ‘he teeth were exceedingly 
numerous, and formed closely compacted regular (?) rows 
reaching back for a distance of probably from a half inch to 
an inch from the anterior extremity of the mouth. They ap- 
* Loe. cit. + Reproduced Pl. VII. fig. 19. 
t I should be glad to be corrected here if I am wrong, as I possibly am. 
