62 GUIDE TO THE FOSSIL REPTILES, AMPHIBIANS, FISHES. 
Classification of Fishes. 
Sub-class I.—ELASMOBRANCHII. Jaw-appara-\ 
tus suspended from skull; no operculum; 
dermal armour without bone-tissue 
Order I.—Acanthodii. All fins except caudal 
with spine in front, and cartilages very- 
short ; no claspers in male 
Order II.—Pleuropterygii. Paired fins sup¬ 
ported by parallel rods of cartilage; no 
claspers in male 
Order III.—Ichthyotomi. Pectoral fins sup¬ 
ported by cartilages radiating from 
central axis; claspers in male . . .. J 
Order IY.—Selachii. Pectoral fins with two or 
three basal cartilages and no central 
axis; claspers in male 
Sub-orders. — Asterospondyli and Tecto- 
spondyli. 
Sub-Class II.—-HOLOCEPHALI. Jaw-apparatus 
fused with skull; an opercular membrane ; 
dermal armour without bone-tissue 
Order I.—Chim^roidei. Fins as in Selachii / 
Sub-class III.—DIPNOI. Jaw-apparatus fused ^ 
with skull; an opercular bone; dermal 
armour often with bone-tissue . . 
Order I.— Sirenoidei. Scaly fishes with paddle- [ 
shaped paired fins, these supported by 
a segmented axis .. . . . . / 
Order II.—Arthrodira. Armoured fishes, the \ 
head-shield hinged on body-shield; 
paired fins rudimentary 
Elasmobranchii 
or 
Chondropterygii. 
Dipnoi. 
Sub-Class IV.—TELEOSTOMI. Jaw-apparatus 
suspended from skull; an opercular bone; 
dermal armour often with bone-tissue 
Order I.— Crossopterygii. Paired fins paddle¬ 
shaped and fringed with fin-rays 
Sub-orders.— Haplistia, Bhipidistia, Actin- 
istia, and Cladistia 
Order II.— Actinopterygii. Supports of paired 
fins much shortened and dermal rays 
chiefly supporting membrane . . 
Sub-orders.— (Jhondrostei, Protospondyli, 
Aetheospondyli, Isospondyli (in part),, 
Isospondyli (continued), Ostariophysi,) 
Apodes , Anacanthini, Percesoces, Semi- > 
branchii, and Acanthopterygii. I 
Ganoidei. 
Teleostei. 
The fossil true fishes are arranged in Gallery No. 6 in 
systematic order according to the above classification, the 
smaller specimens being in the Table-cases, the larger speci¬ 
mens in the Wall-cases. The series begins with the Elasmo¬ 
branchii to the left of the door leading from Gallery No. 4. 
