554 
DR. A. GUNTHER’S DESCRIPTION OF CERATODUS. 
decussating optic nerves. The Holocephala, which differ in several important points 
from the other Chondropterygians, approach the Ganoids by these very characters, and 
are an intermediate form. Furthermore, all those modifications which show an ap- 
proach of the ichthyic type to that next above it, are found in Ganoids and Chondro- 
pterygians, none in Teleosteans ; and, finally, the early coexistence and development of 
Ganoids and Chondropterygians in geological epochs, when no (or only very few) Teleos- 
teans existed, is a circumstance which seems to confirm a conclusion arrived at from an 
anatomical point of view only. 
Therefore I would propose, after the separation of the Cyclostomata and Leptocardii , 
to refer the remaining host of living fishes to two subclasses only, viz. the subclass of 
Tcleostei, and one for which the name Paloeichthyes may be used. In order to put the 
preceding statements into a readily comprehensible form, I have prepared the following 
synoptical table, in which, at present, reference is made to those fossil genera only which 
approach most closely the Dipnoi : — 
First subclass : LEPTOCARDII. 
Second subclass : CYCLOSTOMATA. 
Third subclass : TELEOSTEI. 
Fourth subclass : PALOEICHTHYES. Heart with a contractile conus arteriosus ; 
intestine with a spiral valve ; optic nerves non-decussating. 
Order I. Chondropterygii. 
Suborder 1. Plagiostoma. 
Suborder 2. Holocephala. 
Order II. Ganoidei. 
Suborder 1. Amioidei. 
Suborder 2. Lcpidosteoidei. 
Suborder 3. Polypteroidei. 
Suborder 4. Chondrostei. 
Fam. a. Acipenscridce. 
Fam. 1). Polyodontidce. 
Suborder 5. Dipnoi. Nostrils two pairs, within the mouth. Limbs with 
an axial skeleton. Lungs and gills. Skeleton notochordal. 
No branehiostegals. 
Fam. a. Sirenidce. Caudal fin diphycercal ; no gular plates. Scales 
cycloid. Two pairs of molars and one pair of vomerine 
teeth. 
Subfamily Ceratodontina. Conus arteriosus with transverse 
series of valves. Ovaries transversely lamellated. One 
continuous vertical fin: Ceratodus [ Cheirodusl ]. 
