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XXI. On the Osteology of Polyodon folium. 
By Thomas William Bridge, B.A., Scholar of Trinity College, and Demonstrator of 
Comparative Anatomy in the University of Cambridge. 
Communicated by Alfred Newton, M.A., F.R.S., Professor of Zoology and 
Comparative Anatomy in the University of Cambridge. 
Received May 29, — Read June 20, 1878. 
[Plates 55-57.] 
This G-anoid appears to have been first described, under the name of Squalus spatula, 
by Maduit in the ‘ Journal de Physique’ for 1774, pp. 384-386, plate 2, fig. 1. Sub- 
sequently, several zoologists described and figured the external appearance of Polyodon 
under the various synonyms of Polyodon (Lacepede), Spatularia reticulata (Shaw), 
and Planirostra (Lesueur). The systematic position of the genus appears to have 
changed as often as its name. Originally regarded as an Elasmobranch, and sub- 
sequently as a Teleostean, it was reserved for H. Muller, in 1846, to elucidate its 
real affinities and to indicate its marked distinctness from the other families of Ganoids 
by establishing the suborder Chondrostei for its reception. 
The osteology and myology of Polyodon have received comparatively scanty attention. 
The following are the chief memoirs relating to its anatomical structure with which 
I am acquainted : — 
I. ‘ Spatulariarum Anatomiam clescripsit Tabulaque illustravit Albertus Wagner. 
Berolini, 1848. 
II. The male and female urino- generative organs are described by Hyrtl. 
(‘ Geschlechts-u. Harnwerk bei den Ganoiden.’ Denkschriften der K. Akad., 
Wien. Yol. iii.) 
III. Owen gives a brief description of the structure of the skull in the ‘ Osteological 
Catalogue of the Museum of the Royal College of Surgeons, London.’ Yol. i. 
IV. Huxley also briefly describes the cranium in his ‘ Lectures on the Y ertebrate 
Skull,’ Lecture XI., p. 202, and in his ‘ Anatomy of Yertebrated Animals,’ 
pp. 139-140. 
V. Traquair (■' The Ganoid Fishes of the British Carboniferous Formations,’ Part 1. 
— Palceonisciclce) refers to the structure of the quadrato-pterygoid cartilage in 
Polyodon, and also supplies some interesting facts relating to the arrange- 
