Dr. R. H. Traquair — On Chondrosteus acipenseroides. 249 



outline of the results derived from the study of the specimens in both 

 Miiseums. 



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

 shield have been recognized 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, post- 

 frontals, 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.) 



Fig. 1. — Cranial shield of a specimen of Chondrosteus in the Museum of Practical 

 Geology, Jermyn Street. On the left side the displaced operculum {oj}.) is seen 

 overlapping the post-temporal {pt.) and outer supra-temporal [st.]. 



joining each other in the mesial line, and each is flanked externally 

 by a rather larger squamosal (sq.), the "'mastoid" of a bygone 



