Dr. JR. H. Traquair — Fossil Fish from Borough Lee. 249 



the volcanoes of that country, the presence of which is difficult of 

 explanation in any other way than as an original constituent of the 

 primitive magma. Silica, lime, magnesia, iron, alumina, and even 

 soda, might be explained when abundant, as being taken up from 

 the rocks traversed, but this is not the case with potash. 



Lastly, this theory will explain that constant, continuous, though 

 small supply of magma that is necessary for the never-ending 

 ejections of Stromboli, or the dribbling of lava that goes on almost 

 uninterruptedly at Vesuvius. 



At any rate, it seems that we have in this theory a more satisfac- 

 tory explanation of terrestrial phenomena acceptable alike to the 

 tectonic geologist as to the vulcanologist. 



III. — Notice of New and little known Fish Remains from the 

 Blackband Ironstone of Borough Lee, near Edinburgh. 



No. VI. 



By Dr. R. H. Traquair, F.R.S., F.G.S. 



Ctenodus interruptus, Barkas. 



Ctenodus interruptus, T. P. Barkas, Scientific Opinion, vol. ii. 1869. 



,, „ A. S. Woodward, Ann. Rep. Yorks. Phil. Soc. 1889, pi. i. f. 2. 



THIS interesting species has hitherto been known only by the 

 single type-specimen, a mandibular tooth, contained in the York 

 Museum, originally described by Mr. T. P. Barkas, and recently 

 very correctly redescribed as well as figured by Mr. A. Smith Wood- 

 ward. It so happens that some years ago a considerable number of 

 these teeth, both mandibular and palatal, occurred in the Borough Lee 

 ironstone : my own collection contains no less than forty specimens, 

 and there are many others in the Museum of Science and Art, so 

 that I may now add considerably to the knowledge of the species. 



Mr. Woodward finishes his description as follows : — "As remarked 

 by Mr. Barkas, the tooth thus described is distinguished from the 

 teeth of the most nearly allied species, C. cristatus, by the compara- 

 tive smoothness of the inner moiety of each ridge, and by the 

 distinct separation of the much compressed denticles." But the 

 York specimen is only one of a very variable series of forms, and, 

 of the characters here given, only one is constant, namely, the com- 

 pression of the denticles in a direction at right angles to that of the 

 ridges. Sometimes this character is only very distinctly marked at 

 the outer margin of the tooth-plate, or on its posterior two-thirds, 

 but it is nevertheless seen with absolute constancy in all specimens 

 in which the denticulation is not entirely removed by abrasion, as is 

 sometimes the case. The " comparative smoothness of the inner 

 moiety of each ridge," though a frequent, cannot be said to be a 

 constant character, as I have specimens both mandibular and palatal 

 in which the ridges are denticulated up to their origins, while on 

 the other hand the ridges may be almost entirely smooth until close 

 to the outer margin of the tooth. It is clear that this condition, 

 instead of being specific, is entirely dependent on the amount of 

 abrasion to which the tooth has been subjected in performing its 



