Manchester Memoirs, Vol. Ix. (1916), No. % 29 



these is very large and its anterior end articulates with a 

 pair of large plates which themselves support an azygous 

 plate in front. 



Dipterus platyceplialus, Pan d er. 

 The structure of the roof of the skull, of the palate 

 and of many other parts of the large fish whose remains 

 occur abundantly in exquisite preservation, although in 

 a disarticulated state, in the neighbourhood of Thurso, 

 has been clearly described by Agassiz, Hugh Miller, 

 Pander, Giinther and Traquair. We give for the sake of 

 comparison, a figure {Text-fig. 8. B) of the roof of the 

 skull drawn from specimens in the Museum from the 

 East Shore, Thurso. It will be noticed that this skull and 

 the others which have been figured from the same horizon, 

 differ from that described above from the Stromness 

 Beds in the absence of the posterior row of three plates, 

 which seem in them to have fused with those in front. 

 Otherwise the two types have a great general resemblance. 

 The large series of such specimens in the Museum, allows 

 us to add somewhat to the accounts of the palate given 

 by previous authors. The large skull here figured is 

 unique in the fact that the well ossified brain case is 

 scarcely if at all crushed. It shows a basi-cranial region 

 whose posterior end is excavated by a large conical pit for 

 the anterior end of the notochord. Its lower surface is 

 not markedly convex, but is provided with a median ridge 

 separating a pair of shallow grooves in each of which lies 

 a small foramen. In this specimen the lower surface of 

 the basis cranii is soon faulted down, but is shown, by a 

 comparison of this and other specimens, to be covered by 

 the posterior end of the rhomboidal parasphenoid which 

 does not cover the whole of its lower surface. The lateral 

 surface of the brain case rises vertically from the edges of 



