THE CRANIAL OSTEOLOGY OF RHIZODOPSIS. 169 
History” for April of the present year (1877). ‘In the present communication I 
propose, with the aid of a few restored outline drawings, to consider the entire 
subject of the cranial osteology of Rhizodopsis, the greater part of the material 
for which belongs to the collection of Mr Warp. My thanks are also due to 
Mr Joun Puant of Salford, for the loan of a number of shale specimens, showing 
isolated bones, from the Manchester coal-field. 
Rhizodopsis sauroides, Williamson, sp. 
Cranium proper.—The cranial roof bones form a “buckler,” which in its 
configuration and composition is very similar to that in Osteolepis, Megalichthys, 
&c. As in these forms it falls into two principal parts, anterior and posterior, 
of which the posterior, or parietal portion, is slightly longer than the anterior 
or fronto-ethmoidal. The parietal portion is 
about twice as broad posteriorly as it is in front, 
each external margin passing, a little behind 
the middle, first inwards at an obtuse angle and 
then nearly straight forwards; the anterior and 
posterior margins are nearly straight. This 
portion of the buckler is composed of six paired 
ossifications, two of which (pa. fig. 1) extend 
along its whole length, articulating with each 
other in the middle line; their form is rather 
narrow and elongated, and they are also broader 
behind than in front. These two plates may 
very safely be reckoned as the parietals; as 
such the corresponding plates have been, in 
Ostevlepis and Megalichthys, designated by Pan- 
Fic. 1.—Upper Surface of the Head of 
DER, by HUXLEY in Glyptolemus, and by AGASSIZ Rhizodopsis swuroides. 
F 5 s.¢. supratemporal ; pa. parietal; sq. squa- 
nN Osteolepis, although the last-named author has peal : Df. réatauioe Aéagal ; frontal 
or. orbit ; p.mex. premaxilla. 
marked the very same bones in MMegalichthys 
as “frontals.” Along the outer edge of each parietal are two smaller plates, 
anterior (pf) and posterior (sq.), regarding the signification of which, in 
allied forms, some pretty serious difference of opinion is found in the works 
of different writers. By Agassiz the anterior one was, in Osteolepis, con- 
sidered to be the post-frontal, the posterior to be the “mastoid,” while 
in Megalichthys, he considered the very same plates to be equivalent to 
the chain of intercalary ossicles placed along the external margins of 
the cranial shield in Polypterus. By PanpeEr the latter interpretation is 
accepted both for Osteolepis and Megalchthys; while by Professor Hux ey, 
these two plates, anterior and posterior, are in Glyptolemus respectively termed 
