eumer ss 
VII.—On the Cranial Osteology of Rhizodopsis. By Ramsay H. Traquair, 
M.D., F.R.S., Keeper of the Natural History Collections in the Museum 
of Science and Art, Edinburgh. 
(Read May 21, 1877. Received for Press July 22, 1881, Abstract in ‘‘ Proceedings,” vol. ix. p. 444.) 
In a paper by Mr E. W. Binney on the Fossil Fishes of the Pendleton Coal 
Field, published in 1841, the dentary bone of Rhizodopsis is figured as the 
“upper jaw of a new species of Holoptychius,” to which, however, he did not 
attach any specific name. In the same paper its scales are also figured and 
referred to the same genus.* Scales belonging to the same fish were after- 
wards figured by Professor WILLIAMSON under the name of WHoloptychius 
sauroides,t and again by Mr Satter, as those of Rhizodus granulatus.{ Both 
of these specific names occur under Holoptychius in AGassiz’s general list of 
Ganoids published in 1843, but as they were unaccompanied either by figures 
or descriptions, it is really immaterial which of them, if indeed either, was 
applied by him to the fish in question. The authority for the term “sauroides” 
as applied to the common species of Ahizodopsis, the only species of the genus 
which is as yet known with certainty, must therefore remain with Professor 
Wiuiamson. Holoptychius sauroides of Binney § and of Messrs Kirkby and 
Atthey || is quite another fish, now also distinguished generically as Strepsodus, 
and for it the specific name “ sawrozdes” is therefore equally valid. 
In 1866 Professor Younc published a description of the entire fish, under 
the name of Rhizodopsis sauroides, Williamson, sp., the authorship of the new 
generic title being attributed to Professor Huxtey.' From Professor Youna’s 
description, we learn that the position of Ahizodopsis, in Professor Hux ry’s 
classification of the Ganoids, is in the cycliferous division of the Glyptodipterine 
family of the suborder Crossopterygide, and that it possesses subacutely lobate 
pectoral fins, two dorsals, and a heterocercal tail. Some of the bones of the 
head are noticed, such as the parietals, the three dermal plates of the occipital 
region, the opercular bones, the maxilla, and the mandible. No preemaxilla 
* Trans. Geol. Soc. Manchester, vol. i. (1841), pp. 153-178, pl. v. figs. 6, 8, and 10. 
+ “On the Microscopic Structure of the Scales and Dermal Teeth of some Ganoid and Placoid Fish,’ 
Phil. Trans., 1849, p. 457, pl. xlii. figs, 21-23. 
t “Tron Ores of Great Britain,” Mem. Geol. Survey, 1861, p. 223, pl. i. figs. 4-6. 
§ Op. cit., pl. v. fig. 7. 
|| Trans. Tyneside Nat, Field Club, vol. vi. (1863-64), p. 234, pl. vi. figs. 5 and 6, 
{1 “Notice of New Genera of Carboniferous Glyptodipterines,” Quart. Journ. Geol. Soc., 1866, 
pp. 596-598. 
VOL, XXX. PART I. 2c 
