REVIEWS. 



279 



In this table it will be seen that Professor Huxley adds the suborder 

 (III.) Ceossopteeygid^ (fcpoo-o-ooTos TTTepv^, " fringed fin") to those pro- 

 posed by Agassiz to comprise the existing Polypterus and all those extinct 

 ganoids which fall within the following definition : — 



" Dorsal fins two, or, if single, mnltifid or very long ; the pectoral, and usually 

 the ventral, fins lobate ; no branehiostegal rays, but two prmcipal, 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 

 i3culptu.red." 



The fifth family also has been added by the Professor for that singular 

 genus PlianeropJeuron, described and figured in this decade. 



Of the group of Crossopterygidse, as thus established, four families are 

 not only palseozoic, but are some wholly and all chiefly confined to rocks 

 of the Devonian age, — an epoch in which no fish of the sub-orders 

 Amiadce or Lepidosteid(E is known to make its appearance, unless 

 Cheirolepis be one of the latter. liapidly diminishing in number, the 

 Crossopterygidffi seem to have had several representatives in the Carboni- 

 ferous age ; but after this period, unless Ceratodus be a Ctenododipterine, 

 they are continued high in the Mesozoic age only as a thin though conti- 

 nuous line of Coelacanthini, and terminate at the present day in the two 

 or three known species of the genus Polypteriis, 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 

 Crossopterygida? 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 : — 



Palaeozoic. 



Ctenodijderini, Phaneropleuriniy Glyptodipterini, Saurodipterini. 



/ 



Ccelacanthmi. y 

 Mesozoic. 



1 



Coelacanthini. 



/ 



Tertiary. ^ 

 Recent. / 



Polypterini/ 



Here it is obvious, that in time the Polypterini are twice as remote from 

 their immediate zoological affines, the Saurodipterini and Glyptodipterini, 

 as they are from their more distant connections, the Coelacanthini. 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, 



