ON THE CRANIAL OSTEOLOGY OF RHIZODOPSIS. 179 
elements of the cranial buckler, is on the surface almost entirely obliterated. 
These circumstances would lead us to the conclusion that the Saurodipterini 
constitute a more specialised type than the Cyclodipteride, in which, in a 
previous essay,* I have included the genera Rhizodus, Rhizodopsis, Strepsodus, 
Archichthys, and Tristichopterus, the Glyptolemini being probably intermediate. 
Note added July 20, 1881.—For the term “ Cyclodipteride,” which I have 
hitherto used for the family to which Rhizodopsis, Rhizodus, &c., belong, and 
which I borrowed from Dr LitrTxen (“ Begrenzung und Eintheilung der 
Ganoiden,” German edition, p. 47), though excluding the Holoptychii, which 
were also here placed by him, I propose in future to substitute “ Rhizodon- 
tide,” as being in every way more appropriate. 
* “On the Structure and Affinities of Tristichopterus alatus,” Trans. Roy. Soc. Ed., 1874. 
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