44 
sary. The Dipnoi henceforth form a part of the Ganoid 
order, whose definition is extended to include fishes having 
longitudinal valves in the hulbus arteriosus. The efiect of 
the inclusion of the Dipnoi upon the subdivision of the 
Ganoid fishes will be discussed in a subsequent communica- 
tion. 
Dr. Giinther proposes a further step — to unite the recon- 
stituted order Ganoidei with the Elasmobranchii, so as to 
form a new sub-class — Palceichthyes. Solid reasons are 
adduced for this step, but its discussion is not needful in this 
place. The Ganoidei and Dipnoi must in any case be united, 
and their place is plainly next the Elasmobranchii. That 
the relations of the three groups are close will not be disputed 
by any zoologist. 
Dr. Giinther supplies us with the following list of living 
Ganoids :-^One species of Amia, from North America ; three 
species of Lepiclosteus from the same region, but extending 
southwards into Central America and Cuba ; two species of 
Polyioterus (Galamoichthys) from the tropical parts of 
Africa ; two species of Folyodon, from the Mississippi and 
the Yangsekiang ; about twenty-five Sturgeons, from the 
temperate and subarctic regions of the Northern Hemis- 
phere ; two species of Ceratodus from tropical Australia ; 
one species of Lepidosiren from the Amazon river ; and one 
of Protopterus from tropical Africa. 
From this list alone it would almost be possible to recon* 
struct the general history of the Ganoid order. This groups 
anciently marine as well as fluviatile, is now restricted to 
fresh waters, for even the Sturgeons are essentially riter- 
fishes. The wide distribution of the existing Ganoids shews 
their extensive development in past ages ; their scatteted 
habitat, as well as the extraordinary richness in types of an 
order numerically so scanty, shew that we are contemplating^ 
not the members of a recent colony, but the dispersed relics 
