40 A SYNOPSIS OF ANIMAL CLASSIFICATION. 



Class I. PISCES Aquatic Anamnia, with branchial 



respiration. Paired limbs in the 

 form of fins (ichihyopierygid). 

 Integument generally produces 

 scales, which contain bony ma- 

 terial produced by the corium. 

 Heart with one auricle and one 

 ventricle. 

 Order i. Selachii (Elasmobranchii) .. Skeleton cartilaginous, 



scales placoid. Tail heterocercal. 

 5-7 separate gill openings without 

 operculum. 



X Squalus, Raja, ChimcBra. 



Order 2. Ganoidei Skeleton more or less reinforced 



by bone. Scales typically rhom- 

 boid in form and with a hard pol- 

 ished surface (= ganoid). Tail 

 heterocercal. Gill-slits with oper- 

 culum. X Acipenser, Lepidosteus^ 



Order 3. Dipnoi Skeleton mainly cartilaginous. 



Notochord persistent. Paired fins 

 with a central skeletal axis and 

 with or without lateral rays. 

 Median fin continuous around tail. 

 Swimming-bladder functions as 

 lung. Gills with operculum. In 

 one species small external gills 

 also. A very small, but iso- 

 lated group, including 3-4 living 

 species. 



X Ceratodus, Protopterus. 



Order 4. Teleostei Skeleton mainly osseous. Scales 



cycloid or ctenoid. Tail homo- 

 cereal. Gills provided with an 

 operculum. 



Class II. AMPHIBIA Skin naked, very glandular and 



slimy. Gills, external and inter- 



