500 Dr. E. H. Traquair on the 



proportional extent of the proximal segment of each. Con- 

 sequently the articular and marginal plates of that segment 

 are of greater length than in those two genera ; but what is 

 more remarkable is that the anconeal element (PI. XVIII. 

 fig. 4, a) is reduced to a small rounded plate on the dorsal, 

 and apparently entirely wanting on the ventral aspect of the 

 limb ; so that beyond the articulars the marginals are entirely 

 in contact with each other on the ventral side, and only sepa- 

 rated towards their extremities on the dorsal. In so far as 

 the proximal joint is concerned the limb of Botliriolepis may 

 be said to be simpler in construction than in Pterichthys ] but 

 this is not true of the distal part, in wliich both the central 

 and marginal rows contain each at least one additional plate. 

 Tail. — It is remarkable that no tail is seen in Botliriolepis^ 

 although numerous specimens both of B. canadensis and B. 

 liydropldlus seem perfect in every other respect. It is there- 

 fore perfectly plain that caudal scales were absent, though it 

 does not seem to me quite so safe to assume that no caudal 

 appendage was ever present ; for the posterior aspect of the 

 carapace shows a large opening just as in Pterichthys, out of 

 which it is difficult to conceive that absolutely no body- 

 prolongation ever proceeded, and it does seem quite possible 

 that a tail might have existed, though unprovided with hard 

 ]mrts capable of preservation. Moreover, in a specimen of 

 B. canadensis in the Edinburgh Museum there is to be seen, 

 just at the place where the tail occurs in Pterichthys, a pecu- 

 liar dark organic-looking film, which is strikingly suggestive 

 of the remains of such an appendage. 



British Species o/" Botliriolepis. 



B. hydrophilus, Kg. sp. {y=-Pamphractus hydrophilus and 

 Andersoni, Ag. ; Homothorax Flemingii, Ag. ; Pterichthys 

 hydrophilus, Miller, Egerton). — This interesting form, re- 

 markable for its occurrence in great numbers crowded to- 

 gether in the Dura- Den fish- bed, was elevated by Agassiz 

 into a genus distinct from Pterichthys, but on mistaken 

 grounds, as he compared what was in reahtj the ventral sur- 

 face of that genus with the dorsal one of the present subject. 

 The error of this diagnosis having been seen by Hugh 

 Miller and Sir Philip Egerton, hydrophilus was restored by 

 them to Pterichthys, to which, indeed, Agassiz himself had 

 first of all referred it. 



Recently, however, on carefully developing the specimens 

 on a portion of Dr. Anderson's original slab, now in the Edin- 

 burgh Museum, I was interested to find that this species 



