42 Proceedings of the Royal Fhysical Society. 



parts 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 of Bothriolepis. 



B. hydrophilus, Ag., sp. {=i Pamphractus hydrophilus and 

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

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

 able for its occurrence in great numbers crowded together in 

 the Dura Den fish-bed, was elevated by Agassiz into a germs 

 distinct from Pterichthys, but on mistaken grounds, as he 

 compared what was in reality the ventral surface 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 Pter- 

 ichthys, to which, indeed, Agassiz himself had first of all 

 referred it. 



Eecently, 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 

 does not belong to Pterichthys after all, but is an unmistak- 

 able Bothriolepis, closely allied to B. canadensis. This is at 

 once apparent from the restored figure of its upper surface 

 which I have given on PI. II., Fig. 4. It differs some- 

 what in the sculpture of the plates, which is delicately 

 pitted-reticulate, while in B. canadensis it retains rather more 

 of a confluent tubercular character over most parts of the 

 carapace. The proximal joint of the arm seems also slightly 

 longer in proportion to the distal, and the denticulation of 

 its outer margin rather coarser. 



It is quite obvious that, as Hugh Miller and Sir P. Egerton 

 have already pointed out (8, pp. 311 and 314), Homothorax 

 Flemingii, Ag. (4, tab. xxxi., fig. 6), is founded on a bad 

 drawing of the under surface of the species under considera- 

 tion. 



B. major, Ag., sp. {^Pterichthys major, Ag. ; Placothorax 

 paradoxus, Ag.). — This has been already referred to Bothrio- 



