BALISTIDJ3. 
567 
pelvic fins represented by a pair of stout, moveable spines ; one 
large dorsal spine, followed by about threo very small and com- 
paratively slender spines ; posterior dorsal and anal fins low but 
considerably extended; caudal fin rounded. Dermal tubercles small 
and shagreen-like. 
The uame Acanthopleurus was preoccupied by Acanthopleura, 
Guilding, in 18119, but may be retained until the extinct species 
placed here are satisfactorily known. 
Acanthopleurus serratus, Agassiz. 
1842. Pleuracanthus serratus, L. Agassiz, Poiss. Foss. vol. ii. pi. Ixxv. 
figs. 1,2. 
1844. Acanthopleurus serratus, L. Agassiz, tom. cit. pt. ii. p. 25.3. 
1844. Acanthopleurus brevis, L. Agassiz (ex Egerton, MS.), tom. cit. 
pt. ii. p. 253 (name only). 
1859. Acanthopleurus brevis, G. vom Hath, Zeitschr. deutsch. geol. Ges. 
vol. xi. p. 131, pi. v. fig. 4. 
1859. Acanthopleurus serratus, G. vom Rath, ibid. p. 1 32, pi. v. fig. 5. 
1886. Acanthopleurus serratus, A. Wettstein, Fischfauna lertiaer. 
Glamerschief. (Denkschr. schweiz. Palaeont. Gos. vol. xiii.), p. 47, 
pi. viii. figs. 1-4. 
Type. Imperfect fish ; British Museum. 
The type species, attaining a length of about (PI 2. Maximum 
depth of trunk contained about three times in length of vertebral 
column, which comprises 19 vertebrae. Anterior dorsal spine 
nearly straight, tuborculated, its length about equal to maximum 
depth of trunk; posterior dorsal fin arising at middle point of 
back ; pelvic spines tuborculated, as long as anterior dorsal spine. 
Form. Loc. Oligocene : Canton Glarus, Switzerland. 
P. 454, P. 3974. Type specimen in counterpart, described and 
figured by Agassiz, loc. cit. ; Engi. The fossil is much 
elongated by distortion. Egerton 4' Enniskillen Colls. 
P- 1893, P. 4522. Three imperfect specimens, one being in counter- 
part ; Engi. Egerton dp Enniskillen Colls. 
P. 1892. Imperfect impression of small fish, intended to be the 
type specimen of A. brevis ; Engi. Egerton Coll. 
P- 524. Another imperfect impression. Purchased, 183 / . 
The following oxtinct species, which is not represented in the 
Collection, also appears to belong to Acanthopleurus : — 
Frotobalistum omboni, A. de Zigno, Mem. Soc. Ital. Sci. [3] vol. 
