AND ON THE CLASSIFICATION OF FISH. jon 
The: Cyclostomi, on the other hand, merely resemble the 
Plagiostomi in the undivided cephalic cartilage and the spi- 
racula; in all other respects they differ from them, especially in 
the complete absence of gill-arches; of the jaws; the organs of 
generation having no oviduct or seminal duct; the complete 
absence of the muscular tunic; in the arterial trunk or dulbus 
aorte, and in their two arterial valves. 
The Prince of Canino* has correctly conceived the peculiarity 
of the Rays, Sharks and Chimere, in forming them into a sub- 
class under the name of Elasmobranchii, whilst he included the 
Cyclostomi as one of his four subclasses under the name of 
Marsipobranchii. I agree in this arrangement; but the other 
subclasses, Lophobranchii, the Pomatobranchii (the latter in- 
cluding the orders Sclerodermi, Gymnodontes, Sturiones, Ga- 
noidei, Ctenoidei, Cycloidei), are not confirmed by the present 
state of our knowledge of the anatomy of the osseous fishes and 
the Ganoids. 
Although I admit the subclass Marsipobranchii or the Cyclo- 
stomi, I do not include the Amphioxus in it: from the investi- 
gations which I have already published, I draw the conclusion, 
that it cannot be admitted into any known order or subclass 
of fishes, although it comes nearest to the Cyclostomi in the 
absence of the jaw and the structure of the skeleton. The 
grounds which prevent this are the muscularity of the entire 
vascular system without the presence of a heart, a character not 
found in other fish, nor even in any other of the vertebrata; the 
position of the gills in the ventral cavity, with a respiratory 
abdominal pore; the absence of any distinction between the 
brain and spinal cord; the reduction of the liver to a blind 
sac of the intestine, and the ciliary motion diffused over all the 
mucous membranes. It is the type of a distinct subclass, which 
I name Leptocardii. 
Those fishes which have scales, with both lungs and gills and 
perforated nares, form also a separate subclass, Dipnoi, Nob. ; 
Lepidosiren belongs to it. The valves are longitudinal and spiral, 
and are situated in the muscular bulb of the aorta. ‘The intes- 
tine has spiral valves, as we find in the Plagiostomi, the Ga- 
noids, and some Cyclostomi. The oviduct opens into the 
abdomen ; their vertebral column possesses a chorda with apo- 
| physes. 
* Selachiorum Tab, Analytica, 1838. 
VOL, IV. PART XVI. 2@ 
