CLASSIFICATION OF DEVONIAN FISHES 441 
of the teeth, and the form of the lower jaw in the two families pre- 
senting many curious analogies. 
The Glyptodipterine family contains, as we have seen, both 
cycliferous and rhombiferous genera. Following out the alliances of 
the former subfamily, we have found reason to include the cyclifer- 
ous Ctenododipterini and the cycliferous Ccelacanthini in the same 
larger, or subordinal, group with the Glyptodipterini. If, on the 
other hand, we now trace out the congeners of the rhombiferous 
subfamilies, we arrive, as has been seen, at the Saurodipterini, 
and the question now remains, What other rhombiferous Ganoids 
naturally arrange themselves at this end of the series ? 
So far as I am aware, there is no other fossil rhombiferous Ganoid 
which comes within the scope of the sum of characters common ot 
Fig. 15. Figure of Polypterus (after Agassiz). 
the Saurodipterini, Glyptodipterini, Ctenododipterini, and Ccelacan- 
thini; but among recent fishes there is one, Polypterus, which very 
nearly approaches the required standard, and is unquestionably 
closely allied to the Saurodipterini. 
Polypterus, in fact, has an elongated body, with a depressed 
head, and a conically tapering caudal extremity. The orbits are 
situated in the fore part of the head, while the gape extends far 
back. There are two large principal jugular plates, without lateral 
or median plates. The pectoral arch is covered inferiorly by two 
triangular osseous plates, which meet in the middle line, and 
are superficial to the so-called coracoids. The pectoral and ventral 
fins are lobate. The caudal fin is rhomboidal and nearly diphycercal.! 
A comparison of these characters with those which have been 
assigned to Glyptolemus, or to Osteolepis, reveals at once the close 
connexion of the three genera,? from which however Polypterus 
differs in many important particulars. 
1 See the careful account of the tail of Polypterus, by Kolliker, ‘ Ueber das Ende der 
Wirbelsiule der Ganoiden.” 
* I do not know that any one has hitherto pointed out in detail the very close relation 
between Polypterus and the fossil genera enumerated above; but Professor Pander has 
