350 Proceedings of the Royal Physical Society. 



gical Society of London, of which an abstract has been pub- 

 lished. In this paper Mr Davis interpreted the appearances 

 presented by a single fine specimen in his own collection, 

 and besides giving a detailed account of its anatomical 

 structure, expressed his belief " that there is no specific 

 difference between C. aciyenseroides, Agassiz, and C. crassior, 

 Egerton." 



Mr Davis does not seem, however, to have made use of the 

 magnificent suite of specimens of Chondrosteics in the British 

 Museum, which contains not only the types of Sir Philip 

 Egerton's figures, but also a splendid array of additional 

 examples, mostly also from the Egerton and Enniskillen 

 Collections. For the privilege of examining these, and of 

 noting several new and interesting details presented by them, 

 I am indebted to Dr Woodward, F.R.S., Keeper of the Geo- 

 logical Department; and my thanks are due also to Dr 

 Geikie, F.R.S., and Mr E. T. Newton, F.G.S., for kindly per- 

 mitting me to take notes of the specimens in the Museum of 

 Practical Geology, Jermyn Street. In the present paper I 

 propose to give an outline of the results derived from the 

 study of the specimens in both Museums. 



Cranial Shield. — The elements of the main portion of the 

 cranial shield have been recognised by Sir P. Egerton and by 

 Mr Davis, the former of whom enumerates ''the parietals, 

 the mastoids, the frontals, and the prefrontals," — the latter 

 stating that the " frontals, postfrontals, parietals, mastoid, 

 and some of the occipital plates are present." This cranial 

 shield is exhibited in many of the British Museum specimens, 

 but in none have I seen it better displayed than in one 

 belonging to the Museum of Practical Geology, from which 

 Fig. 1 has been taken. Here we have two oblong parietals 

 (p.) joining each other in the mesial line, and each is flanked 

 externally by a rather larger squamosal {sq), the " mastoid " 

 of a bygone nomenclature. In advance of the two parietals 

 are two large frontals (/.), also in apposition mesially, while 

 posteriorly, and externally, each of them also touches the 

 squamosal of its own side. Then, occupying a corner between 

 the hinder part of the external margin of each frontal and 

 the anterior external margin of the corresponding squamosal, 



