6 1 2 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 Sirenoidei and the Arthrodira. 

 We follow Dean in regarding the latter as representative of a 

 distinct class, leaving the Sirenoidei, 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 Diplopneunioiui, with the lung divided. To the 

 latter order the Lcpidosirenidcv belong. To the former the 

 Ccratodontidcc, 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 UronemidcB 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, as in Amia. The few species are found 

 in the Carboniferous, Uronemus lobatus being the best-known 

 species. 



In Dipteridce 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. 



