June 26, 1896.] 



SCIENCE. 



911 



and innumerable deviations from the typi- 

 cal fish form are developed. 



But, as Dr. Dean well observes, the fish 

 form ' is a factor in the evolution of fishes 

 which appears in [almost] every [large] 

 group and subgroup. And it has ever 

 stood in the way of classifying them satis- 

 factorily according to their kinships ' (p. 7). 

 Still more aggressive as obstacles have been 

 certain deviations from that form and especi- 

 ally the eel-like form. The anguilliform 

 modification, resulting from elongation of 

 the body and concomitant adjustments, 

 such as union of the vertical fins, loss of 

 the ventrals, and restriction of the bran- 

 chial apertures, is apt to recur in various 

 groups, and does occur in the plectospondy- 

 lous ' eels ' (' electrical eel, ' etc.) and the 

 symbranchoid to such a degree that it has 

 been difficult even for ichthyologists to con- 

 vince themselves that the likeness was de- 

 ceptive as indication of afiinity. 



The progress of ichtliyologj^ has been in a 

 ratio inverse to the influence on the mind 

 of this ancient concept of the importance of 

 adaptation of the organization for aquatic 

 life. Many are still influenced by it. As 

 a consequence all the branchiferous verte- 

 brates are confounded in one class — the 

 Fishes or Pisces. By most morphologists, 

 however, that physiological group is sub- 

 divided into three or more classes. Three 

 are admitted by Dr. Dean — the Leptocar- 

 dians, the Marsipobranchs, and the true 

 Fishes or Pisces. The last two are arran- 

 ged in the following table (p. 8): 



A CLASSIFICATION OF FISHES. 



Type : CHORD ATA (Vebtebkates). 



Class : Maesipobeanchii, Lampreys, Palssospon- 



dylus, Hag, Lamprey, Ostracodcrms. 

 Class : Pisces (true fishes). 

 I. Sub-class : Elas.mobeanchii, Sharks and 

 Eays. 

 Order: Pleuropterpr/ii, (Dean), Cladoselachids 

 (Dean). 

 " IcMhxjotomi (Cope), Pleuracanihids. 

 " Selaohii, Sharks and Eays. 



II. Sub-class : Holocephali, Chimreroids, 

 Spook-fishes. 

 Order : Chimieroidei, Squaloraiids, Blyriacmi' 

 tJtids, Chimisrids. 

 in. Sub-class : Dipnoi, Lung-fishes. 



Order : Sirenoidei, Dipterids, Phaneropleuridg, 

 Ctenodonis, Lepidosirenids. 

 ' " ? Arthrodira, C'occosteids, ilylostomids. 



IV. Sub-class : Teleostomi, Ganoids and Bony 

 Fishes (Teleosts). 

 Order : Crossopterygii, Holoptychiids, Osteole- 

 2nds, OiiycJwdonts, Ccelacanthids. 

 ' ' Actinopterygii. 



Sub-order : Chondrostei (Ganoids), Paliconis- 

 colds, Sturgeons, Garpikes, Anli- 

 oids. 

 " Teleocephali, recent Bony Fishes 

 (Teleosts). 



In this table Dr. Dean claims to have 

 ' retained in the main the classification of 

 Smith Woodward,' but he has adopted the 

 most prominent features from Prof. Cope. 

 It expresses, too, the ideas of most mor- 

 phologists, but it is questionable whether 

 Dr. Dean has gone far enough in the valua- 

 tion of some groups. The reviewer would be 

 inclined to admit four classes exclusive of 

 the Leptocardians. 



The ' Marsipobranehii ' might be split into 

 two classes — the Marsipobranehii (properly 

 classed) and the Ostracophori or 'Ostra- 

 codcrms ' as Dr. Dean calls them. The 

 latter are very imperfectly unknown, and 

 only by Prof Cope had they been previously 

 associated in the same class as the Marsipo- 

 branchs. By Woodward they wei-e ranked 

 as a special subclass of true fishes. The 

 evidence for any allocation is defective but 

 for the present the group may be given 

 class rank and retain the name Ostracophori. 

 It was originally named Ostracodermi,but 

 that name having been preoccupied (in 

 1872) by Gill for the Ostraciids, the new 

 name was later given by Cope. But 

 although first distinguished as a subclass 

 under the name Ostracodermi, the dif- 

 ferences between the representatives of that 

 subclass and the Arthrodira had been to a 



