of Edinburgh, Session 1877-78. 
G57 
Monday, 20 tli May 1878. 
DAVID STEVENSON, Esq., C.E., Vice-President, 
in the Chair. 
The following Communications were read : — 
1. On the Genus Rhizodus. By Dr R. H. Traquair. 
(Abstract.) 
In this paper the author first sketches the history of Rhizodus, 
from its discovery by Ure of Rutherglen to the most recent papers 
on the subject. 
Placed by Agassiz among the “ Coelacanthi ” (i.e., cycliferous 
Crossopterygia of modem nomenclature) it was classified by Professor 
Huxley in the cycliferous division of his family Glyptodipterini, 
along with Holoptychius , Glyptolepis, Dendrodus. The discovery 
by the author, in 1875, of its subacutely lobate pectoral fin revealed 
the fact that it was much more closely allied to Rliizodopsis than to 
Holoptychius, and that it ought, along with the former genus, to be 
classed in a family (Cyclodipterini) distinct from the acutely lobate 
Holoptychiidae. The author does not consider the identity of 
Leidy’s genus Apepodus with Rhizodus as proved. 
M‘Coy admitted two species of Rhizodus — R. Hibberti , Agassiz, 
and R. gracilis , M‘Coy, merging with the former of these the Holop- 
tychius Portlockii of Agassiz. An examination of the types of 
Holoptychius Portlockii, preserved in the Museum of Practical 
Geology, shows, however, that this species is not only specifically 
but also generically distinct from Rhizodus Hibberti , as the teeth are 
devoid of the cutting edges characteristic of Rhizodus, and in this 
particular, as well as in the minute striation of the surface, they 
closely resemble those of Hancock and Atthey’s genus Archichthys , 
to which the author proposes to transfer it, at least provisionally. 
An investigation of the large store of Rhizodus remains from the 
Gilmerton ironstone, belonging to the Edinburgh Museum of Science 
and Art, shows the presence of two well-marked species of Rhizodus, 
differing in the bulk to which they attained respectively, as well as 
in the relative thickness of the scales, the shape of many of the 
