250 Dr. R. H. Traquair — Fossil Fish from Borough Lee. 



masticatory functions ; for as a general rule it is less marked in the 

 smaller than in the larger specimens. And also, as a rule, the 

 palatal teeth seem to have suffered more from this tear and wear 

 than the mandibular ones. 



Ctenodus interruptus is still more variable in its form than Ct. 

 cristatus ; in fact hardly two of the numerous specimens which I 

 have seen can be said to be alike. Some are proportionally longer, 

 others broader in their shape ; in some the ridges are more trans- 

 verse, in others more radiating in their direction, and, as above 

 noticed, the extent to which the ridges are tuberculated displays 

 a wide range of variation. The number of ridges on the type- 

 specimen is fourteen, two being intercalated at the margin ; but 

 the usual number upon the mandibular tooth is eleven or twelve, 

 though in one case they are reduced to nine. Bifurcation or inter- 

 calation of the ridges is also common in mandibular teeth, and indeed 

 at the posterior extremity of the tooth-plate they often appear alto- 

 gether broken up into groups of tubercles. In the palatal teeth the 

 ridges are usually more regular, and their number varies from twelve 

 to fifteen. A portion of the hinder part of the cranial roof shows 

 that the median occipital plate was pointed in front, as in Ctenodus 

 cristatus. 



Although it is not difficult to tell a specimen of C. interruptus from 

 one of C. cristatus by the general appearance, and indeed at the first 

 glance, it is nevertheless by no means easy to put into words a set 

 of characters which shall absolutely separate the two from each 

 other. The only absolutely constant feature of C. interruptus is the 

 compression of the denticles in a direction at right angles to the 

 ridges ; but I have before me now a mandibular tooth of 0. cristatus 

 from Newsham which does also to a slight extent exhibit that 

 character as well as the comparative smoothness of the inner moiety 

 of the ridges. And it must also be pointed out that the " type " 

 specimen is not very typical in its shape, as the majority of specimens 

 have a considerably greater resemblance to C. cristatus. I have 

 therefore been for years in a state of doubt as to whether C. inter- 

 ruptus should be retained as distinct, but the absolute constancy of 

 the peculiar compression of the outermost denticles in all those 

 Lower Carboniferous specimens certainly seems to be a justification 

 for calling them by a different name from that of their close relatives 

 in the Coal-measures. 



The type-specimen of C. interruptus is said to be from Gilmerton ; 

 it is contained at all events in a piece of undoubted Scotch Lower 

 Carboniferous ironstone. I have, however, never myself met with 

 a specimen in the Gilmerton ironstone, though that of Borough Lee 

 and Loamhead has yielded so large a number. It occurs also in the 

 Carboniferous Limestone series at Kinghorn, Fifeshire ; in the 

 Calciferous Sandstone series at Pittenweem in the same county ; 

 and at West Calder, Midlothian. In the west of Scotland it has 

 occurred in the ironstone of Barkip, Dairy (Carboniferous Limestone 

 series), specimens from that locality existing in the collections of 

 Mr. E. Craig Beith and Mr. John Smith. 



