15 



CLASSES. 



The classes thus recognized may be distinguished as follows, the char- 

 acters used, however, being supplemented by many others: — 



I. Skull more or less developed, with the notochord not continued forwards beyond 



the pituitary body. Brain differentiated and distinctly developed. Heart 

 developed and divided at least into an auricle and ventricle. 



A. Skull well developed, and with a lower jaw. Paired fins developed (some- 



times absent through atrophy) ; and with a shoulder girdle 1 (lyriform or 

 furcula- shaped, curved forwards and with its respective sides connected 



below 2 ), and with pelvic elements. Gills not purse-shaped. 



PISCES. 



B. Skull imperfectly developed and with no lower jaw. Paired fins unde- 



veloped, with no shoulder girdle nor pelvic elements. Gills purse-shaped. 



MARSIPOBRANCHII. 



II. Skull undeveloped, with the notochord persistent and extending to the anterior 



end of the head. Brain not distinctly differentiated. Heart none. 



LEFTOCABDII. 



SUBCLASSES OF PISCES. 



The most diverse views have been urged within the last few years in re- 

 gard to the combination into major groups or subclasses of the orders of 

 the true fishes, Profs. Kner, 3 Owen, 4 Liitken, 5 and Cope 6 on the one hand 

 combining the Teleosts and Ganoids into one group or more closely ap- 



1 The shoulder girdle of the Elasmobranchiates appears to be homologous with the 

 paraglenal or coracoid elements (ride postea) of the specalized fishes, the proscapula 

 of the latter having been apparently first developed by exostosis in the Ganoids, and 

 finally become preponderant while the paraglenal became proportionately reduced. 



2 This character distinguishes the class Pisces from the Batrachia. 



3 Kner (Rudolph). Betrachtungen iiber die Ganoiden, als natiirliche Ordnung. 



• • • . <Sitzungsberichte der Kaiserlichen Akademie der Wissenschaften. — 



Mathematisch — Naturwissenschaftliche Classe, b. 54,1. abth., 1866, pp. 519-536. 



Prof. Kner concludes with the expression of belief that the Ganoids do not form a 



homogeneous group, and should not, therefore, be retained in the system, and that, 



far from being an improvement, the introduction of the group was a hindrance to 



the progress of Ichthyology. 



4 Owen (Richard). On the Anatomy of Vertebrates, v. I, 1866, p. 7; also, v. Ill, 



186S, p. 854 (Zoological Index). 



The fishes (Pisces) are divided (in v. I.) into (1) Subclass I. Dermopteri (includ- 

 ing Pharyngobrauchii and Marsipobranchii) ; (2) Subclass II. Teleostojii ; (3) Sub- 

 class III. Plagiostomi ; (4) Subclass IV. Drrxo.v : Subclass V. Monopxoa is equivalent 

 to the class Reptilia elsewhere (p. 6) admitted by him. 



In the Zoological Index, the author reverses the sequence, and designates the 

 "Dipnoi" as a simple order (order Protnpleri), placing it at the head of the class 

 Pisces. 



6 LiJTKEN (Christian). Prof. Kner on the Classification of the Ganoids 



<The Geological Magazine (London), v. 5, 1868. 



