■ CHAPTER IX. 



DIPNOI.* 



Scaly fish with gills ^ and lungs, external and internal nares, 

 cartilagirious autostylic skull covered with osseous dermal scutes, 

 persistent notochord with unsegmented sheath, and with an oper- 

 culum covering the gill apertures. Paired fins ivith long segmented 

 cartilaginous axes. Caudal fin diphycercal or heterocercal. 

 Branch iostegal rays absent. Heart with spirally twisted conus 

 arteriosus. Palatal and mandibular teeth few, tuberculated, 

 as though made up of fused denticles. The mid-brain roof is not 

 divided into optic lobes. 



The important characters of the Dipnoi are the pecuhar teeth, 

 the acutely lobate often fringed paired fins, the autostylic skull, 

 the internal opening of the nasal sac, the cartilaginous endo- 

 skeleton almost devoid of cartilage bone, the persistent uncon- 

 stricted notochord and absence of vertebral bodies, the conus 

 arteriosus, the incipient doubleness of the heart, and the 

 presence of a vein resembling the inferior vena-cava. In conse- 

 quence of the form of the skull, the vascular system and breathing 

 arrangements, the possession of an internal as well as of an 

 external opening of the nasal sac, the nature of tlie egg and the 



* Owen, Lepidosiren, Trans. Lin. Soc. 17, 1840. Hyrtl, Lepidosiren 

 paradoxa, Prag, 1845. Gvinther, Ceratodus, Phil. Trans, 161, 1872. 

 Huxley, Ceratodus, Proc. Zool. Soc, 1876, p. 24. Bridge, Skull of Lepi- 

 dosiren, Trans. Zool. Soc, 14, 1897 ; p. 325. Fritsch, Fauna der Gaskohle, 

 Bd. 2., 1888. Lankester, Hearts of Ceratodus, Protopterus, etc.. Trans. 

 Zool. Soc. 10, 1879, p. 493. Boas, Herz u. Arterienbogen bei Ceratodus 

 n. Protopterus, Morph. Jahrb., 6, 1890, p. 321. W. N. Parker, Anatomy 

 of Protopterus, Trans. R. Irish Acad., 30, 1892, p. 109. Spencer, Blood- 

 vessels of Ceratodus, Maclay memorial volume, Lin. Soc. N.S.W.. 1893. 

 Ehlers, Zur Kenntniss der Eingeweide v. Lepidosiren, Nach. K. Gesellsch. 

 d. W. zu Gottingen, 1895. R. Burckhardt, Das Centralnervensystem v. 

 Protopte7-us annectens, Berlin, 1892. Kerr, External Featvu-es in the 

 de^^elopment of Lepidosiren, Phil. Trans., 192, 1900, p. 299. Semon, 

 Papers on Ceratodus by different authors in Zoologische Forschungsreisen 

 in Australien etc. Jena, 1898. 



