184 
PROFESSORS T. W. BRIDGE AND A. C. HADDON 
Exostoma BJythii, Day. 
Of this Siluroid, Day (9) says : — “ Air-vessel in a globular form, on either side of 
the body of the anterior vertebra?, and enclosed in bone.” 
Group : — Aspredinina. 
Aspredo coUjlophonis. 
This South American genus is regarded by Cope (7) as the type of a distinct 
finnily (Aspredinidse) of the order Neraatognathi (= Siluridae). The only reference 
to the air-bladder of Aspredo that we are acquainted with is by CuviEii and 
Valenciennes in their ‘ Histoire Naturelle des Poissons,’ vol. 15, 1840. The air- 
bladder of Aspredo Icevis” (= A. hatrachus) is there briefly described as composed 
of two ovoid lobes with fibrous Avails of a silvery lustre. 
In Aspredo cotylophorus the skull, Avith the first, the complex, and the fifth 
A'ertebrae, are immovably connected together. The body of the first \-ertebra 
(figs. 73, 74, vd) is fairly Avell-developed, though somewhat smaller than the normal 
centra, and so obliquely placed, that its anterior and posterior concavities are 
directed foi'w^ards and downwards and backwards and upAvards respectively (fig. 74). 
The complex centrum (figs. 73, 74, c.c.) is unusually long and narroAV, and is, more- 
over, so bent upon itself that Avhile its deep and almost tubular posteiaor concavity 
looks directly backAvards, its cup-shaped anterior face is directed doAvnwards as Avell 
as forwards to meet the upturned posterior face of the centrum of the first vertebra 
(fig. 74). The centrum of the fifth vertebra {vd) is almost as long, and its deep 
tubular anterior concavit}^ is in striking contrast to the relatively shallow posterior 
concavity. The sixth vertebra (fig. 73, p.'’) is quite free and distinct from the fore- 
going; its short transverse processes carry the first pair of ribs. 
The neural arches of the complex and fifth vertebra? (fig. 74) are almost completely 
confluent. The coalesced spinous processes of the third and fourth vertebra; 
(figs. 74, 75, n.sd, n.sd) are re|)i-esented by a low, compressed ridge of bone of 
uniform height, but greatly thickened along its free dorsal margin. The anterior 
edge of the ridge, Avith the neural arch of the third vertebra, incline forAvards to a 
firm sutural union Avith the supraoccipital and exoccipitals, Avhile the posterior 
margin considerably OA’erlaps, and partially coalesces Avith, the sjnne of the fifth 
vertebra. The latter (?ls.^) is very strongly developed, inclined obliquely backAvards, 
and cleft foi- the support of the anterior interspinous bones. 
The transverse processes of the fourth and fifth vertebra; (figs. 73 to 75, t.pd, t.pd) 
combine to form on each side a narroAv Aving-like outgroAvth, Avhich is much longer 
than broad, slightly concave from before backwards on its ventral surface, and has its 
anterior and posterior margins strongly thickened and produced distally into free 
