DIPNEUSTI 5 I I 



not in a nest, but singly amongst aquatic vegetation, and, as 

 they are not adherent, it is probable that they finally rest on 

 the mud. The early developmental stages exhibit a general 

 resemblance to those of Amphibia. There is no larval meta- 

 morphosis, and at no period does the young Neocemtodus (Fig. 

 305) possess cutaneous gills or a cement organ. The tail is 

 apparently diphycercal from the first, and the pelvic limbs do 

 not appear until about six weeks after the pectoral members. It 

 is interesting to note that the dental plates are first represented 

 by lines or patches of separate denticles (non-ctenodont), which 

 subsequently fuse basally (ctenodont) before the adult condition 

 is reached. 1 Neoceratodus is stated to grow to a length of 5 to 6 

 feet. 



Fam. 4. Lepidosirenidae. Body elongate, cylindrical and 

 more or less Eel-like, with small cycloid scales completely en- 

 closed in the skin. Paired fins so acutely lobate as to present 

 the appearance of tapering cylindrical filaments, equally devoid 

 of scales and fin -rays. In a general way the cranial dermal 

 bones correspond with those of Neoceratodus, but the place of the 

 posterior median bone is taken by a large, gable-like fron to- 

 parietal bone, situated internal to the head muscles, and in direct 

 relation with the chondrocranium, which is largely aborted in 

 the interorbital region. Circumorbital bones absent. Opercular 

 bones much reduced. Lower jaw without dentary plates. Palatine 

 and splenial dental plates with three non-denticulate, trenchant 

 ridges. Hyoid arch consists of cerato-hyals only. Hyoidean 

 cleft closed. Certain of the anterior branchial arches devoid 

 of branchial filaments ; when present the latter are leaf-like and 

 free. Air-bladder a double lung. There is a larval meta- 

 morphosis, and the young possess cutaneous gills. The family 

 includes two genera, Protopterus and Lepidosiren. In the former 

 genus the paired fins are either uniserial or they consist of axial 

 mesomeres only ; there are six branchial arches and five clefts ; 

 and the larval gills are usually retained as vestiges throughout 

 life. In Lepidosiren the paired fins are reduced to the segmented 

 axis, without pre- or post-axial radials. There are five branchial 

 arches and four clefts, and the cutaneous gills disappear soon 

 after the larval metamorphosis. 



Protopterus has a wide distribution over the middle portion of 



1 Seiuon, op. cit. p. 115. 



