EEVIEWS. 
279 
In this table it will be seen that Professor Huxley adds the suborder 
(III.) Ceossopteetgidje (KpoaracoTos TTTepv^, " fringed fin ") to those pro- 
posed by Agassiz to comprise the existing PolT/pteriis and all those extinct 
ganoids which fall within the following definition : — 
" Dorsal fins two, or, if single, nmltifid or Terr long ; the pectoral, and usually 
the reiitral, fins lobate ; no brancliiostegal rays, but two principal, with sometimes 
lateral and median jugidar plates, situated between the rami of the mandible ; 
caudal fin diphycercal or heterocercal ; scales cycloid or rhomboid, smooth or 
sculptured." 
The fifth family also has been added by the Professor for that singular 
genus PJianeropleuron, described and figured in this decade. 
Of the group of Crossopterygidae, as thus established, four families are 
not only palaeozoic, but are some wholly and all chiefly confined to rocks 
of the L)evonian age, — an epoch in which no fish of the sub-orders 
Amiadce or Lepidosteidce is known to make its appearance, unless 
Clieirolepis be one of the latter. Eapidly diminishing in number, the 
Crossopterygidae seem to have had several representatives in the Carboni- 
ferous age ; but after this period, unless Ceratodushe a Ctenododipterine, 
they are continued high in the Mesozoic age only as a tiiin though conti- 
nuous line of Coelacantliini, and terminate at the present day in the two 
or tliree known species of the genus Polijpterus, which however is clearly 
related to the rhombiferous Crossopterygians, or to exactly that group of 
whose existence we have no knowledge in any Mesozoic or Tertiary 
formation ; while the Ctenododipterini and Coelacanthini, which differ 
most widely from Polypterus, are those which continue the line of the 
Crossopterygidae from the Palaeozoic to the end of the Mesozoic period. 
Both ends of the Crossopterygian series appear thus to be isolated from 
the modern representatives of the suborder : Polypterus being separated 
from those members of its suborder with which it has the closest zoological 
relations by a prodigious gulf of time, and from the fossil allies which are 
nearest to it in time by deficient zoological affinity. Professor Huxley 
offers the following diagram in illustration of his meaning : — 
Paleozoic. 
Ctenodipierini, Phaneropleurini, Gli/j)todipterini, Sa2'.rodipteri77i. 
Ccelacanthini. ^ 
I Mesozoic 
1 
CcElacanthini. 
/ 
Tertiary. ^ 
Recent. / 
Pohjpterini/ 
Here it is obvious, that in time the Polypterini are twice as remote from 
their immediate zoological aflines, the Saurodipterini and Glyptodipterini, 
as they are from their more distant connections, the Ccelacanthini. Pro- 
fessor Huxley calls attention to the many and singular relations subsisting 
between that wonderful and apparently isolated fish, Lepidosiren, sole 
member of its order, and the cycloid Glyptodipterine, Ctenododipterine, 
