194 
DAVIS : OSTRACACANTHUS DILATATUS. 
ferous age, namely the Elasmobranchii and the Ganoidei. In 
the genus Ostracacanthus, if the diagnosis I have attempted 
should be substantiated by further discoveries, there is 
evidence that fishes closely allied to some of the more 
abnormal forms of the Teleosteans of the present day existed 
during that period. Prof. Huxley, in The Tenth Decade of 
the Memoirs of the Geological Survey, has expressed the 
opinion that several of the fishes of the Devonian rocks are 
closely related to the modern Siluroids. In the structure of 
the head of Coccosteus, the general arrangement of the bony 
exoskeleton much resembles that of the tropical fish Clarias; 
whilst the peculiar form of the mandibles, and the expansion 
of the bony elements usually considered to be homologous 
with the coracoid and radius of other fishes, so as to form a 
large ventral shield, offers many points of resemblance to the 
Siluroid, Loricaria. The Devonian Pterichthys is also in 
several ways closely related with the modern Siluroids. Its 
osseous envelope can only be compared to the box-like 
cincture of the modern Ostracion ; and the fossil fish Cepha- 
laspis has also certain resemblances to Callichthys and 
Loricaria. Prof. Huxley remarks that "at any rate I think 
the prima facie case in favour of the Teleostean nature of 
Coccosteus is so strong that it can no longer be justifiable 
to rank it among the Ganoids, - sans phrase,' but that even 
those who will not allow it to be a Teleostean must attach to 
it the warning adjunct of incerta sedis." And further, " Why 
should not a few Teleosteans have represented their order 
among the predominant Ganoids of the Devonian epoch, just 
as a few Ganoids remain among the predominant Teleosteans 
of the present day ? When it is considered that an ichthy- 
ologist might be acquainted with every fresh-water and 
marine fish of Europe, Asia, South Africa, South America, 
the Indian Archipelago, Polynesia and Australia, and yet 
know of only one Ganoid— the sturgeon — a fish so unlike the 
