522 Notices of Memoirs — Dr. R. E. Traquair's Address. 



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in many things, such as that the Crossopterygii were not derived 

 from the Dipnoi, and that the modern representatives of the latter 

 group are degenerate forms, yet as to the immediate ancestry of 

 the Dipnoi themselves, and the diphyletic origin of the so-called 

 archipterygium, we had best for the present keep an open mind. 



In his " Catalogue of the Fossil Fishes " in the British Museum 

 (vol. ii, 1891) Dr. Smith Woodward, following the suggestion of 

 Newberry in 1875, classified the Coccosteans or ' Arthrodira ' as an 

 extremely specialized group of Dipnoi. At first I was much taken 

 with that idea, but after looking more closely into the subject 

 I began to doubt it extremely. My own opinion at present is that 

 the Coccosteans are Teleostomi belonging to the next order, Actino- 

 pterygii ; but Professor Bashford Dean, of New York, will not have 

 them to be even ' fishes,' but places them in a distinct class of 

 ' Arthrognatha,' which he places next to the Ostracophori (=Ostraco- 

 dermi), even hinting at a possible union with them, whereby the 

 old ' Placodermata ' of McCoy would be restored. It will, therefore, 

 be better to leave them out of consideration for the present, pending 

 a thorough re-examination of their structure and affinities. 



We come then to the great order of Actinopterygii, to which 

 a large number of the fishes of later Palgeozoic age belong, as well 

 as the great mass of those of Mesozoic, Tertiary, and modern times. 

 Of these we first take into consideration the oldest sub-order, namely, 

 the Acipenseroidei or Sturgeon tribe, in which the dermal rays of 

 the median fins are more numerous than their supporting ossicles, 

 while the tail is, in most, completely heterocercal. The oldest 

 family of Acipenseroids witli which we are acquainted is that of the 

 Palaeoniscidge, which, in addition to well-developed cranial and facial 

 bones, has the body normally covered with rhombic ganoid scales 

 furnished with peg-and-socket articulations. It endures up to the 

 Purbeck division of the Jurassic formation, and in the Carboniferous 

 Cryphiolepis, the Lower Permian Trissolepis, and the Jurassic Cocco- 

 lepis we find the same degeneration of the rhombic scales into those 

 of a circular form and imbricating arrangement, which we find 

 repeated in other groups of ' Ganoids.' 



In these Palaeozoic times we notice also a side branch of the 

 PalEeoniscidee, constituting the family Platysomid^, in which, while 

 the median fins acquire elongated bases, the body becomes shortened 

 up and deep in contour. A most interesting series of foi'ms can be 

 set up, beginning with Uurynotus, which, though it has the platy- 

 somid head contour and a long-based dorsal, has only a slight 

 deepening of the body, and still retains the palteoniscid squamation 

 and a short-based anal fin. In Mesolepis, which resembles Eurynotus 

 in shape, being only slightly deeper, we have now the characteristic 

 platysomid squamation, and the base of the anal fin is considerably 

 elongated. Platysomtis has a still more elongated anal fin, and the 

 body is rhombic ; while in CJieirodus the body is still deeper in 

 contour, with peculiar dorsal and ventral peaks, long fringing dorsal 

 and anal fins, while the ventrals seem to have disappeared altogether. 

 Here also, as in the allied genus Cheirodopsis, the separate cylindro- 



