REPORT ON SPIRULA. 
5 
of the arms are united by a very thin interbrachial membrane, which surrounds the 
buccal disk and does not carry suckers. 
b. Tentacular Arms. —The tentacular arms were retracted in the Challenger specimen, 
but only partly and not completely as in Sepia, Sepiola, &c.; their acetabuliferous 
extremities bent back reach those of the sessile arms (PI. I. fig. 1, T.). The free extremity 
of the “ tentacles ” is pointed, but not widened as in the other Decapods ; the “ supra- 
brachial ” longitudinal ridge is there more elevated and more like a membrane than that 
upon the sessile arms. The remainder of the tentacular arms is rounded and smooth. 
The pocket in which each tentacle is in part retracted is formed by the interior of the 
base of the third and fourth sessile arms as usual, and when the retraction of the organ 
takes place, it is folded back on itself. In this position the tentacle resembles a bent 
arm, the proximal portion (attached) representing a very short arm, while the remainder 
corresponds to a long fore-arm with the acetabuliferous part at the extremity like a hand 
(PI. III. T 1 .). When the tentacular arms are thrown out and extended they are longer 
than the whole body (PL II. figs. 1, 2). The area on which the suckers are situated 
is in the form of an elongated oval, narrowed at the extremity corresponding to the 
summit of the arms, not exceeding one quarter of an inch in length ; the suckers have 
the same form and arrangement as those of the sessile arms, the diameter of the largest 
not exceeding 200th of an inch. 
c. Suckers. —The suckers are “ cups” slightly pedunculated ; their peduncle is not, as 
in Sepia, inserted in the axis of the sucker, but laterally as in the (Egopsids, Loligo, &c. 
(see PI. VI. fig. 10). The largest suckers are found at the proximal extremity (basal) 
of each acetabuliferous area, and do not exceed xtroth of an inch in diameter. They 
gradually diminish in volume up to the summit where their diameter is not more than 
250th of an inch. They are closely crowded over the whole surface of the acetabuliferous 
area, but without perfect regularity; six or seven of them occupy the width upon the 
largest part of the area, while there are not more than three or four at the base of the 
area, and not more than two or three at the summit. Their “ horny ” armature is thick, 
and in a few the form is that of a globular glass without bottom ; the free annular 
border is produced into short spines (see PI. VI. fig. 9 ). 
3 . The Funnel, Muscles, and Cartilages. —The funnel is closed ventrally, as in all 
the Dibranchiates. On the internal cephalic wall is a small anterior valve in the female 
(PI. I. fig. 7 , I.v.). This character also exists in the male. 1 There does not seem 
to be any trace of “ Muller’s organ ” (mucous gland of the funnel) so widespread 
in the Dibranchiates. The infundibular collar (see PI. I. fig. 5 ) is high and not fused to 
the mantle dorsally (PI. IIP). Ventrally, upon the sides of the collar, are linear, elon¬ 
gated, cartilaginous fossae (Pis. I., II., and IV., li.) corresponding to the protuberances of 
1 Steenstrup, Sepiadarium og Idiosepius ( Vidensk. SelsJc. Skr., naturhist. og math. Afd., ser. 6, Bd. i., 
Kjobenhavn, 1881, p. 229). 
