EEYIEWS. 



277 



foriuatioris, until at present its sole representative is the African Poly- 

 pterus. TJie genus wliicli approaelies it most closely is the Gyrojptycliius of 

 M'Cov. Glyptopomus is another closel}^- allied genus, as is evidenced by 

 the structure of its skull. The angles of the scales of G-yroptychius are 

 apt to become rounded off so as to present a transition from the rhomboid 

 to the cycloid contour. It is then the less surprising to find fishes with 

 cycloid scales so similar in their organization to GrlyptolsBmus, Gyropty- 

 chius, and Glyptopomus as imperatively to demand a place near them in 

 any natural arrangement. The description of HoloptycJiius, compared 

 with that of Glyptolsemus, will show their essential alliance, but the scales 

 are inform and sculpture widely different. Platygnathush closely allied 

 to Holoptychius. G-lypiolep'is, with its remarkably ornamented scales, is 

 closely allied to Holoptychius. These six genera, then, possess characters 

 in common, and constitute a family of Ganoids, the Gltptodipteeini, 

 and ^^hich may be subdivided into a rhombiferous group, containing 

 GlyioJcBnms, Glyptopomus, and Gyroptychius, with diphycercal tails ; and 

 a cycliferous group, containing Holoptychius, Platygnathus, and Glypto- 

 lepis. The family of Saueodipteeint, distinct from, although allied to the 

 Glyptodipterini, comprises not only the genera Osteolepis, Diplopterus, 

 and Triplopterus (?), but also. Professor Huxley believes, the Mega- 

 lichthys of the Coal. The Saurodipterini and Glyptodipterini being sepa- 

 rated from other palseozoic fishes as well-defined but closely-allied families, 

 the author goes on to consider what others can be ranged with them, or, 

 in other words, T^ hat are the limits and what the importance of the larger 

 group formed by the association of these families. The Ctenododi- 

 PTEEiNi, a family just established by Pander for the reception of Dipterus 

 and its immediate allies, must, he considers, take its place in close juxta- 

 position to the Saurodipterini and Glyptodipterini, seeing that it possesses 

 all those structural peculiarities which are common to those two families ; 

 but the former differ in the smoothness of their scales and other points, 

 but chiefly in the peculiar form of the lower jaw, which much resembles 

 that of a Coelacanth, and in their dentition. In the next place, the true 

 CcELACANTHiNi liavc a uo Icss well- defined right to occupy a similar position, 

 but the Professor restricts the group to Coelacanthus, Undina, and Ma- 

 cropoma. The type species of Coelacanthus, that on which the genus was 

 founded by Agassiz, is the C. granulatus of the Magnesian Limestone, 

 which in all the great features of its organization is similar to Undina ; so 

 that, contrariwise, any fish which differs in essentials very M-idely from 

 Undina can be uo Coelacanthus. As the case stands, then, there is no 

 evidence of the supposed distinction betv^een CopJacanthus ?mdi Undina; 

 while, on the other hand, a recent comparison of well-preserved speci- 

 mens of Undina and Macropoma has led to the conviction that these two 

 genera are not much less closely allied. All the structural characters 

 which are among the peculiarities of Undina are equally well m.arked in 

 Macropoma, except that the teeth are more distinct and cylindrical. But 

 further than this, as Dr. Mantell originally suspected and as Professor 

 Wilhamson has since demonstrated, Macropoma exhibits the peculiarity, 

 seemingly without a parallel among fishes of other families, of having the 

 walls of its air-bladder ossified. Now Professor Huxley finds good evi- 

 dence of the existence of a similarly ossified air-bladder, not only in 

 Undina, but in a well-preserved specimen of a new genus of Coelacanth* 

 from the Lias, in the Museum of Practical Geology. Thus it appears to 

 be certain that fishes closely allied to Coelacanthus granulatus, forming a 

 w^ell-defined family, have ranged in time, with remarkably little change, 

 * Ho/ophagus Gulo, described in this Decade by Sir P. Egerton. 



