856 The American Naturalist. 
[Oct 
CROSSO PTERYGIA. 
I. Dorsal baseosts present; pectoral axonosts uniserial. 
Pectoral fins a simple axis, when present ; body with 
dorsal and ventral shields; axonosts articulating 
with neural spines; ^Placodet 
Actinotrichia present ; axonosts articulating with neu- 
ral spines ; Haplis 
Median fin radii equal in number and articulating with 
baseosts ; Taxis 
II. 'No dorsal baseosts (or rudiments only) ; pectoral £ 
triserial. 
Median fin radii equal to and articulating with base- 
osts; axonosts not articulating with neural spines ; 
The Placodermi includes the families of the Coccosteidae, and 
'Dinichthyida^. 
The Phaneropleuridae is the only known family of the Hap- 
listia; while two are known to belong to the Taxistia, viz., 
the Holoptychiidcne and the Osteolepididae. To the Cladistia 
belongs only the existing family of the Polypteridai. 
PODOPTERYGIA. 
One order of this superorder is known. 
Median fins with actinotrichia, and with baseosts 
and axonosts corresponding with each other and 
with neural spines ; scapular arch suspended to 
cranium by a post-temporal element ; a precora- 
coid arch and interclavicles ; no preoperculum 
nor symplectic ; a notochord ; Chondrosiei. 
To the order Chondrostei belong three families, the Polyo- 
dontida.^ and Accipenseridae without, and the Chondrosteid^ with, 
branchiostegal radii. 
actinopterygia. 
Two tribes pertain to this superorder. 
Ventral fins abdominal ; a ductus pneumaticus ; no 
""'""'"^ dorsal fin ; parietal bones usually in con- 
Physostomi. 
scales usually cycloid; 
