PROF. OWEN ON NEW AND RARE CEPHALOPODA. 153 
The acetabula are uncinated and of similar structure to each other, differing in little 
else save size, which diminishes as they are situated nearer the free extremity of the arm. 
Their number in the portion preserved (Pl. XXXII. figs. 1 & 3) is fifty, of which four 
have been lost, as shown in fig. 1. They are arranged in a double alternate series, in 
proportional numbers and at nearly proportional distances throughout. This arrange- 
ment, with the size and shape of the hooks, shows that we have not here the acetabulife- 
rous extremity of one of the pair of “ tentacles,” as in Onychoteuthis raptor (Pl. XXIX. 
figs. 1 & 2, 7%). 
Each acetabulum, in Enoploteuthis cookii, consists of a “ pedicle,” a (figs. 4, 5), a cup, 
6, with a horny circular lining, c, produced into the hook, d. The pedicle is conical, 
qo of an inch (=3 millims.) in length in the larger acetabula; its apex is inserted, not 
into the pole, or middle of the base, of the cup, but nearer that side toward which the 
hook is bent, which in most cases is toward the base of the arm. 
The fleshy cup has the form of an irregular, rounded, hollow, truncate cone, of which 
the base is somewhat concave ; and the cavity, excavated for the lodgment of the annular 
basis of the hook, leaves an apical aperture for the protrusion of the uncinate portion. 
The hook is developed, in reference to the sides and the fore end of the supporting arm, 
from the outer and fore part of the border of the horny hoop. 
Now, here it may be remembered that the homologous hoop or partial horny lining 
of the sucking-cup in all Decapods is commonly more or less denticulate at its free 
border, usually minutely so. In many Squids the spines gradually gain length at the 
outer part of the hoop’s margin (Loligo plei, Bl., for example’). The development is pro- 
portionally greater in Loligo brongniartii, Bl’. In Ommastrephes ensifer (Pl. XXVIII. 
fig. 2) the partial development is restricted to fewer spines, but is greater. In Loligopsis 
guttata four of the spines at the outer side of the armed border of the hoop in the 
tentacular suckers are much longer than the rest. In Hnoploteuthis cookii the develop- 
ment is concentrated on one part of the hoop, but is excessive, forming the characteristic 
claw of the genus. 
The base of this hook is so extended as to seem to expand into the horny lining of the 
acetabulum, in the flesh of which it sinks. This lining, soft and whitish at its inserted 
border, becomes corneous (or chitinous) and thickens as it rises above the brim of the 
fleshy cup to form the hook. Of the fleshy or muscular mass the fibres (fig. 4a, fig. 5a, q) 
exterior to the horny ring are circularly disposed, adapted to compress the base of the 
hook and protrude it. The central fibres (ib. f) are longitudinal, and converge to be 
inserted into the hollow base of the hook for its retraction. This action is analogous to 
that by which the ordinary Cephalopods create the vacuum of the sucking-cup in the 
act of adhering to and seizing their prey; but in Hnoploteuthis the base of the hook 
extends too far into the substance of the acetabulum to allow of such retraction, while 
1 D’Orbigny, op. cit. Loligo, pl. xxiv. figs. 17, 18. 2 Thid. Loligo, pl. iv. figs. c & d. 
