528 WALTER EDWARD COLLINGE. 
another, the intervening gaps being but very imperfectly 
bridged over by a series of still less perfect extinct forms whose 
fossil remains show, in most cases, few if any indications of the 
course of this system of canals (20). 
Of the eight known genera of recent Ganoids I have exa- 
mined specimens of all excepting Scaphirhynchus, which 
in all probability is very similar to Acipenser. 
The PoLtyoponTIp# are undoubtedly the most generalised 
family, and most closely related to the Elasmobranchii. 
In the ACIPENSERIIDZ we have a great advance upon any- 
thing seen in either of the genera in the preceding family, and 
yet the absence of mandibular and maxillary branches and the 
persistence of large numbers of primitive pores are features 
which are truly Selachian. Acipenser is the first species in 
the class Pisces in which the canal or its branches enters into 
the cranial elements. 
Of the Teleosteoid Ganoids we have three families widely 
separated from one another. 
The most interesting feature in the LEPIDosTEIDZz is un- 
doubtedly the greatly developed system of dendritic branches 
passing off from the main canal and entering into the various 
cranial elements. These fine branches anastomose and form a 
dense network. In this feature the system resembles in many 
ways that present in the Selachians. There are no branches 
on the lateral canal. In the pre-orbital region there are a 
number of fine branches which anastomose and form a com- 
missure connecting the two supra-orbital branches, a condition 
peculiar to Lepidosteus osseus, so far as is at present 
known (19). 
The Potyrrerip& show a number of features not previously 
met with. In Polypterus (18) we note the absence of dendri- 
form branching and primitive pores, and the small number of 
pores generally, the presence of a branch from the operculo- 
mandibular branch, which passes across the cheek-plate, and a 
fine canal passing through the series of canal bones (= inter- 
calary ossicles of Traquair) which connects the main canal of the 
head with the operculo-mandibular branch. There are also 
