Correspondence — Prof. E. B. Cope — Mr. W. Davies. 141 



surface by consequence of change of shape from the level to the 

 convex. 



The tunnel, opening out at the butt of the Glacier on to the sea- 

 beach, has doubtless been the main outlet for the ground melting, and 

 its arched shape may also be deemed significant of the process of 

 convexity adopted by the contraction of the Glacier from side to side. 



The mechanism may be likened to the curling in of the sides of a 

 piece of wood or paper when the flat side is exposed to the fire, — 

 and it would be all the greater if the other surface were damped, 

 just as the upper surface of the Glacier would be by the rainfall or 

 snowfall of the season. Mr. Melvin's explanation of the formation 

 of the Parallel Boads in Norway valleys may therefore be pro- 

 visionally proposed to be applied to the phenomena of other Glacier 

 actions, but there are many of these probably that have not convex 

 roofs, nor ground tunnels like the Alaska Glacier. W. J. Black. 



United Service Club, Edinburgh, February, 1886. 



EDESTUS AND PELECOPTERUS, ETC. 



Sir. — I observe in your interesting article on the Edestus Davisii, 

 in the January Number of the Geological Magazine, that you refer 

 to the genus Pelecopterus, Cope, as identical with Ptychodus, Agass. ; 

 the pectoral spines representing the former being supposed to belong 

 to the animal whose teeth have given origin to the second name. 



My studies of these fishes have led me to entertain a different 

 opinion from the above. Ptychodus, being a shark, is not likely to 

 have a pectoral arch and fin like that of Pelecopterus. Moreover, 

 these pectoral spines have been frequently found associated with the 

 jaws and teeth of the " snout-fishes " of the Kansas Chalk, which 

 have been described under the generic head of Erisichthe, Cope. 

 Several species are known (see Bulletin U.S. Geol. Survey Terrs, 

 iii. 1877), and one of them is probably the Xiphias Dixoni of Agassiz, 

 from the Chalk of Sussex, England. These genera cannot be re- 

 ferred to any of the existing orders of fishes, on account of the 

 peculiar structure of the pectoral arch. I have therefore placed 

 them in an especial one, the Actinopteri (see Proceedings Amer. 

 Assoc. Adv. Science, 1877(78), p. 299). E. D. Cope. 



Philadelphia, Jan. 26, 1886. 



NOTE ON THE ABOVE, BY MB. W. DAVIES, F.G.S. 



Professor Cope is, I think, mistaken in assigning Xiphias Dixoni 

 to Agassiz. The name first appears in a paper by Dr. Leidy "On 

 Savrocephulus and its Allies," in the Trans. Am. Phil. Soc. vol. xi. 

 p. 91, where the name was given to the prolonged ethmoid bone 

 referred by Sir Philip Egerton to Saurocephalus lanciformis, as then 

 understood. 



In that paper Dr. Leidy proves that the teeth assigned by Agassiz 

 to the Savrocephalus of Harlan had no relation to that genus, and he 

 refers the jaws and teeth from the English Chalk to a new genus ; 

 under the name of Protosphyrmna, Leidy. The "rostral" bones 

 described by Sir Philip Egerton, he contended did not belong to 



