238 Subclass Dipneusti, or Lung-fishes 
of the body, giving a distinct back as well as neck. In the 
spiny-rayed fishes the ““back’’ as well as the neck disappears, 
the pelvic elements being attached to the shoulder-girdle, and 
in a few extreme forms (as Ophidion) the pelvis is fastened at 
the chin. 
Classification of Dipnoans.—By Woodward the Dipneusti are 
divided into two classes, the Szrenotdet and the Arthrodira. 
We follow Dean in regarding the latter as representative of a 
distinct class, leaving the Sirenoidet, with the Ctenodipterini, 
to constitute the subclass of Dipneusti. The Sirenoidei are 
divided by Gill into two orders, the Monopneumona, with one 
lung, and the Diplopneumona, with the lung divided. To the 
latter order the Lepidosirenide belong. To the former the 
Ceratodontide, and presumably the extinct families also belong, 
although nothing is known of their lung structures. Zittel 
and Hay adopt the names of Ctenodipterini and Sirenoidei for 
these orders, the former being further characterized by the very 
fine fin-rays, more numerous than their supports. 
Order Ctenodipterini. — In this order the cranial roof-bones 
are small and numerous, and the rays of the median fins are 
very slender, much more numerous than their supports, which 
are inserted directly on the vertebral arches. 
In the Uronemide the upper dentition comprises a cluster 
of small, blunt, conical denticles on the palatine bones; the 
lower dentition consists of similar denticles on the splenial 
bone. The vertical fins are continuous and the tail diphycercal. 
There is a jugular plate, asin Amia. The few species are found 
in the Carboniferous, Uronemus lobatus being the best-known 
species. 
In Dipteride there is a pair of dental plates on the palatines, 
and an opposing pair on the splenials below. Jugular plates 
are present, and the tail is usually distinctly heterocercal. 
In Phaneropleuron there is a distinct anal fin shorter than 
the very long dorsal; Phaneropleuron andersoni is known from 
Scotland, and Scaumenacia curta is found at Scaumenac Bay 
in the Upper Devonian of Canada. 
In Dipterus there are no marginal teeth, and the tail is 
heterocercal, not diphycercal, as in the other Dipnoans gener- 
ally. Numerous species of Dipterus occur in Devonian rocks. 
