Tilt. COTTOIDS OF NORTH AMERICA. 19 
more compressed than the abdominal ones; this is owing principally to the more 
erect position of the neural arch, and to the presence of hamapophyses, build- 
ing up a hemal arch terminated by hemal spines (hs), also intimately soldered 
together. The anterior hemal arches are very much bent backwards, in the same 
manner as the anterior neural arches, but they soon become less so. The haemal 
canal itself, likewise diminishes backwards. The neural and hzmal spines of the 
last vertebra but one (y) are flattened and expanded. The terminal caudal vertebra 
is reduced to a very small centrum, which seems to be absorbed by caudal plates 
(n' h’), on the edge of which the rays of the caudal fin (d n’) are inserted. The 
upper edge of n’, and the lower of /’ exhibit a rudimentary spine, no doubt the 
first indication of the rudimentary rays of each caudal lobe. 
The ribs themselves or pleurapophyses (p/) are needle-like, a little curved, and 
diminish gradually in length backwards. 
The interneural spines (7 7) are variable in form, stouter under the first dorsal fin. 
The interhzmal spines (7 4) are more uniform. 
The dermo-neural (d m) and dermo-hemal (d h) spines, are all very much alike, 
the only difference consisting in the spiny or bony nature of those belonging to 
the first dorsal fin. 
§ 3. CoMPARISONS BETWEEN THE SKULLS OF DIFFERENT Corti. 
Prare II. Fig. 6—21. 
The skull of C. viscosus (Fig. 6—9) as described above (p. 14) must be recalled 
to mind in order to understand these comparisons. 
The chief difference between C. viscosus and C. Franklinii (Fig. 10—13) consists 
in the fronto-orbital arcade which forms nearly a straight line along the declivity of 
the snout (Fig. 12). Besides, this region is a little shorter than the cranial box 
itself. The upper surface is likewise depressed, and the depression extends back- 
wards on the occiput, so that the latter region appears more convex in Cottus 
Franklinii (Fig. 13). The cephalic channels of the lateral line are more developed 
than in C. viscosus; the upper view (Fig. 10) exhibits very plainly this difference 
by the reduced smooth surface in the middle, and the larger holes along the cireum- 
ference. The acoustic capsule differs also in both of these species. We might even 
notice a difference in shape in the front of the vomer, which, in all the species, bears 
a narrow band of teeth. 
In C. Wilsonii (Fig. 14—17), the fronto-orbital arcade is still lower than in C. 
Franklinii, and passes gradually to the upper surface of the skull without the 
slightest rising above it. This region again is of the same length as the cranial 
box itself. The upper surface of the skull is flat and perfectly even; being a 
little lower near the orbit than on the occiput; it has a slight sloping forwards 
(Fig. 16). This character will likewise be found on those species the external 
appearance of whose snout is rather elongated. Seen from behind (Fig. 17) the 
upper part seems more convex than it is in reality; this apparent convexity being 
given to it by the mastoid crests. 
