XIX DIPNEUSTI sp a 
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 Neoceratodus (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.’ 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 fronto- 
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 Semon, op. cit. p. 115. 
