. The biology of the amphibia. Amphibians. RELATIONSHIPS AND CLASSIFICATION 463 most advanced member of the suborder isLysorophusof the Lower Permian of North America, now known in some detail, thanks to the investigations of Sollas (1920). This genus is frequently referred to as a " Permian urodele," although it retains too many labyrinthodont characters to be considered a near relative of the Caudata. SUBORDER 2. AlSTOPODA.—Among the Carboniferous lepos- pondyls were several genera of legless, long-bodied Amphibia which are grouped here as a distinct suborder. They possessed elonga
. The biology of the amphibia. Amphibians. RELATIONSHIPS AND CLASSIFICATION 463 most advanced member of the suborder isLysorophusof the Lower Permian of North America, now known in some detail, thanks to the investigations of Sollas (1920). This genus is frequently referred to as a " Permian urodele," although it retains too many labyrinthodont characters to be considered a near relative of the Caudata. SUBORDER 2. AlSTOPODA.—Among the Carboniferous lepos- pondyls were several genera of legless, long-bodied Amphibia which are grouped here as a distinct suborder. They possessed elongate skulls, distinctive transverse processes, and peculiar ribs. They were the sirens and amphiumas of the Carboniferous swamps; and even at this early time leg reduction had been car- ried to completion in this one group. SUBORDER 3. NECTRIDIA.—The skull structure of the more primitive genera of Nectridia was close to the embolomerous Fig. 143.—Head of Caecilia tentaculata. Zygosphene-zygantrum articulations were present on the rather elongate neural arches. In the more advanced types as repre- sented by Diplocaulus, the posterior angles of the head are pulled out to form a peculiar, triangular-shaped head. In spite of this specialization, Diplocaulus possessed many primitive features such as a separate coracoid (Douthitt, 1917) and possibly a fifth finger. All other Amphibia except certain Embolomeri have lost the outer finger, and hence the retention of this structure in one suborder of lepospondyls is of interest. SUBORDER 4. GASTROCENTROPHORI.—The salamander or Amphiuma-like lepospondyls of the families Microbrachidae, Hylonomidae, Limnerpetontidae may be grouped together following the lead of Abel (1919), although their relation to each other and to the other suborders is not well defined. ORDER 4. GYMNOPHIONA.—The Gymnophiona or cae- cilians are limbless, long-bodied Amphibia, living today and having no fossil representatives. They resemble large earth-.
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