| 482 The American Naturalist. [May, 
or near the margin ; cranium with the epiotics enlarged, encroaching 
backward and juxtaposed behind, intervening between the exocci- 
pitals and supraoccipatal; prootic and opisthotic represented chiefly 
by the enlarged prootic ; the suborbital chain imperfect ; the copular 
bones separated by intervening cartilaginous elements; the hypo- 
pharyngeals styliform and parallel with the branchial arches, epi- 
_pharyngeals in full number (4 pairs), and mostly compressed ; the 
orsal fin composed of inarticulate rays or spines, separable into 
lateral halves, and the ventrals (when present) sub-brachial. 
myodome may be present or absent, none being developed in the 
Regalecidz, but one being distinct and supplemented. by a dichost in 
the Trachypteride, The families may be briefly differentiated as 
follows : 
TRACHYPTERIDA. 
Teniosomes with the body moderately elongated and very com- 
pressed, the head short, the opercular apparatus abbreviated (the 
REGALECIDÆ. 
Tæniosomes with the body very elongated and compressed, the head 
oblong, the opercular apparatus well developed (the operculum ex- 
tended backwards, the suboperculum obliquely behind it, and the 
interoperculum extended upwards below the two), the preorbital chain 
oblique and widest at the second bones, yentrals represented by single 
elongate rays, the cranium with the myodome atrophied, and the 
dichost suppressed, the supraoccipital pushed forward by the extensive 
development of the epiotics which encroach forwards on the roof as 
well as back and sides of the cranium, and with short ribs.—Turo. 
N. Git. 
The Genera of the Podocnemididz.—Through the kindness 
of Prof. R. Hertwig, of Munich, I have received the skull and cerv- 
icals of two specimens of the type of Emys tracaxa Spix. for exam- 
ination. I am now able to give the characters of the known genera 
of the Podocnemididz. Boulenger considers Emys tracaxa Spix. 
the type of Peltocephalus Dum. & Bibr., and Dumerilia madagascar- 

