Dipnoi — Sirenoidei. 



95 



nostrils more or less within the mouth (Fig. 131, u) ; and the 

 dentition (Fig. 131) consists of a pair of ridged plates above 

 and below, usually with a pair of incisor-like vomerine teeth 

 above. An ordinary bony operculum covers the gill-cavity. 

 The paired fins are acutely lobate, supported by a central 

 jointed cartilaginous stem fringed with radial cartilages and 

 dermal fin-rays. 



The earliest Dipnoi are Lower Devonian. Dipterus (Fig. 

 132) is beautifully presei'ved in the Caithness flagstones, 

 and exhibits two dorsal fins, a heterocercal tail, and enamelled 

 scales. PhaneropleuroH (Fig. 133) occurs in the Upper Old Red 

 Sandstone of Dura Den, Fifeshire, and Scawnenacia in the 

 Upper Devonian of Canada. Gtenodus is characteristic of the 

 Carboniferous and Lower Permian, and is met with both in 

 Europe and America. All these genera are characterized by 

 the roof of the skull exhibiting moi'e numerous bones than 

 that of the living Dipnoi. The teeth of Cerafodns occur in 

 early Mesozoic strata in Europe, India, South Africa, and 

 Central North Amei'ica ; but only one important skull has 



Wall-case, 

 No. 5, and 

 Table-case, 

 No. 34. 



Fig. 1. 31.— Mouth of Ccratodn 



, Hit, narial openings ; x, vomerine teeth ; .a:, palato-pterygoid 

 teeth ; .(;.':.'.■, mandibular teeth. 



been described, this from the Rhgetic of Austria. A tine series 

 of teeth is exhibited from the Rha3tic of Aust Cliff near 



Fig. 132.— Dipterus VaUncltuncni, Sedgw. and Murch. (restored by C. H. Pander); Lower Old 

 Bed Sandstone, Scotland. 



