6 
ACAXTHODII. 
spines broad and robust, much laterally compressed, very slightly 
arched, with one very prominent, oblique, longitudinal ridge and 
groove and several minor grooves ; pelvic fin-spines relatively small, 
scarcely attaining one quarter the size of the pectorals. Pelvic fins 
placed far forwards, the length of the space between this pair and 
the pectorals equalling about one half that of the space between it 
and the anal. Anal fin-spine half as large as the pectoral; dorsal 
still slightly smaller, situated a short distance behind the anal. 
Scales smooth or with a median pit. 
According to the latest memoir on the subject—that by Kner— 
A. bronni is distinguished from the so-called A. gracilis by its less 
slender proportions, its relatively smaller scales, and the more poste¬ 
rior situation of the pelvic fins. The two forms, however, are deter¬ 
mined as occurring together both in East and West Germany; and 
all the examples figured by Kner from Saarbriick (Ehenish Prussia) 
are named A. gracilis. 
An examination of the series of specimens mentioned below, sug¬ 
gests to the present writer that the comparatively robust appearance 
of the type specimens of A. bronni and other fossils in the Saar¬ 
briick nodules assigned to this species is due entirely to imperfect 
preservation. The fishes have been buried in a coiled-up state, 
while the skin with its scales has been displaced by crushing; and, 
when a sharp outline is distinguishable, the body appears quite as 
slender as that of the well-preserved typical examples of A. gracilis 
occurring in the fine shale of Klein Keundorf. The size of the 
scales is also inconstant, and we can therefore, as yet, determine 
only one species in the German Itothliegendes. 
Kner describes, as characteristic of this species, the presence of a 
small spine bounding the posterior margin of the pectoral fin. The 
statement, however, seems to have been based upon a mistake in 
observation; for the specimens in the Collection exhibit no such 
spine, and in one case cited (Kner, pi. v. fig. 1) it may well be a 
fragment of an ordinary pectoral, while in the other case (Kner, 
pi. vi. fig. 1) it is probably the pelvic fin-spine somewhat displaced. 
Form, Loc. Lower Permian (Kothliegendes) : Germany. 
22658 a. A small specimen completely coiled upon itself, in a 
nodule ; Saarbriick, Khenish Prussia. The circum- 
orbital plates and the gill-arches are shown in the region 
of the head. Purchased , 1848. 
40048-50. One nodule with obscure remains of a fish of moderate 
size ; another with remains of a large head and anterior 
portion of the abdominal region; and a third nodule con- 
