5 2 4 SCIENCE PROGRESS 



ptyctodonts, as represented by the genera Ptyctodus, Rhynchodus, 

 Palccomylus, and Rhamphodus. In the British Museum Catalogue 

 of Fossil Fishes the group, of which only three genera were 

 then known, is placed in the chimaeroid order of the Holo- 

 cephali. In a paper on Devonian fishes published in Sitz.-Ber. 

 Ges. nai. Freunde, Berlin, for 1906 (p. yy) Dr. Jaekel accepted this 

 arrangement, with certain modifications. Somewhat later 

 Dr. Dollo {Bull. Soc. Beige Ge'ol., vol. xx. p. 133) denied that the 

 ptyctodonts were Holocephali, although not giving his full 

 reasons for the statement. This was in June, 1906, and a month 

 later Dr. Jaekel (op. cit., p. 180) changed his previous opinion, 

 and classed these fishes in the sturgeon group (Chondrostei). 

 During the present year Dr. Dollo has published a paper (pp. cit. f 

 vol. xxi. p. 1) in which he not only maintains the opinion that 

 the ptyctodonts cannot be classed with the chimaeroids, but 

 goes a step further, and definitely places them in the Arthrodira, 

 that is to say with Coccosteus and its relatives. He also 

 expresses his opinion that the Holocephali are specialised 

 derivatives from the Palaeozoic cochliodont sharks. 



In another paper, on the new genus Pholidosteus and the 

 mouth-opening and bodily form of the Placodermata, published 

 in the Sitz.-Ber. Ges. nat. Freunde, Berlin, 1907 (p. 170), Dr. 

 Jaekel reiterates the views expressed by him in 1902 in regard 

 to this group. Our readers may be reminded that under the 

 title of " Placodermata " the author unites the Ostracodermata 

 (Pteraspis, etc.) with the Arthrodira (Coccosteus, etc.), although 

 by most authorities the two latter are widely separated. 

 Dr. Jaekel regards all the placoderms as true fishes, which, 

 apart from the retention of certain ancestral features derived 

 from amphibians, are related to the Holocephali (chimaeroids), 

 Elasmognathi (sharks and rays), and Chondrostei (sturgeons), 

 with some indications of kinship to the Dipnoi (lung-fishes). 

 These groups he would brigade together under the title of 

 Hypostomata, in contradistinction to the Teleostomata, which 

 include all other fishes. 



The list of these primitive fishes has been augmented by 

 Mr. E. Hennig's description, in the Centralblatt filr Mineralogie, 

 1907, p. 584, of a new species from the Palaeozoic rocks of 

 Gerolstein, referred to the genus MacropetalichtJiys (an ally of 

 Astcrolepis), with the name M. pelmensis. 



