sIRKNfilDEl. 321 



Subclass II. DIPiNOI. 



Fishes with the skeleton partly cartilaginous, partly 

 osseous; no occipital condyle. Bulbus arteriosus 

 with two longitudinal valves ; air-bladder double, 

 lung-like, communicating by a duct and glottis with 

 the haemal side of the oesophagus, with a pulmonary 

 vein. A narrow gill-opening on each side, with a 

 rudimentary gill-cover ; some of the branchi/J arches 

 Avithout gills; gills free, membranaceous. Nostrils 

 double on each side. Intestine with a spiral valve. 

 Optic nerves not decussating. Oviducts distinct. 

 Ventral fins abdominal. 



Clr. Miiller, Abhaiull. Ak.AViss. Berlin, 1 S44, p. 2<)1 ; Owen, Aiiat. 

 Vortebr. i. pp. 8, 14. 



On(> family only — 



SIRENOIDEI. 



Body eel-shaped, covered with cycloid scales. Vei'- 

 tical fins a continuous border to the compressed ta- 

 pering tail. Pectoral and ventral fins subulntc. A 

 single maxillary dental plate is opposed to a single 

 mandibular one. Scapular arch attached to the occi- 

 put. Vent not in the median line. No pseudo- 

 bran chise. 



Freshwater fishes of tropical Africa and America. 



Two genera are known : — 



Three external branchial appendajres I. Protopti'-rvs, p. .■!•_'•_'. 



Xo oxternal branchial appiMulatres "J. 1-ki'11)osii{k\. p. H-J.l. 



