234 
w: f«£3to, i^^'L 
/<?*$ f>-$/3 . 1949. 9^^ 
= /kLv-^ 
DIPNOI- 
f3♦. tkt. ^ -/. f*^cj 
i°aJ.^*r^T2i 
/<-*^^ O ^ ( . . . J.... . » - , 
ft"**. Skeleton partially ossified, with numerous well-developed mezn-= 
C/ .CV^W/A. 2 ?brane bones. Upper mandibular arch confluent with the chondro- 
£•/ v 8 f*> cranium; gill-clefts feebly separated, opening into a cavity with 
external cover. Exoskeleton consisting of true bony tissue. In the 
living forms—optic nerves not decussating, bulbus arteriosus of the 
heart with series of valves, intestine with a spiral valve, and air- 
bladder lung-like. 
The dermal or membrane bones of the cranial roof in this subclass 
exhibit little conformity with the arrangement almost invariably 
observed in the Teleostomi; and it seems impossible to apply to 
them the nomenclature adopted in the case of the latter subclass. 
Fig. 36. 
Dentition of extinct Dipnoi.—1. Dipterus valenciennesi, Sedgw.&Murch.; upper 
and lower jaws, nat. size, xx, upper dental plates; xxx, lower dental 
plates ; g , upper dentigerous bones ; n, narial openings. 2. Ctenodus cris- 
tatus, Ag.; tipper dental plates (somewhat inaccurately drawn, the oral 
aspect being in reality concave), one-third nat. size. 3. Sagenodus in- 
(Bqualis, Owen ; lower dentition, one-half nat. size. 4. Palesdaphus insignis, 
Tan Ben. & De Kon, ; lower dentition, one-sixth nat, size. 
