PROF. OWEN ON NEW AND RARE CEPHALOPODA. 133 
a short course to make way for the third supplementary row, which extends along the 
mid line of the acetabuliferous area to the attenuated terminal fourth part of the arm, 
where the biserial arrangement is resumed. A few suckers at the filamentary termi- 
nation of the arms fall into the single series with which they began to appear at the 
base. 
All the suckers are sessile. Each expands into a circular disk, the border of which is 
soft and thick; and therefrom converge a series of thin folds, opening into a central 
cavity which expands towards the bottom, whence rises a caruncle like the piston of a 
syringe. The mechanism of the Poulpe’s sucker is here repeated. The disk being 
applied to the surface to be seized, the piston is retracted, and the resultant vacuum 
converts the disk into a sucker’. The number of the suckers of a third arm (3) is 268: 
there is not more disparity of size between them than in the common Poulpes’. 
The mantle, or body-tunic, is continued into that of the head along the basal 
breadth of the dorsal aspect of the body (Pl. XXIII. fig. 1, ¢); it terminates an- 
teriorly and ventrally in a thickish free margin. From this wide aperture the 
‘“‘funnel” or respiratory tube projects; its base is not attached or articulated by cup- 
and-ball lateral cartilages, as in Decapoda; consequently it is more freely movable 
from side to side, and is commonly seen to project from one or other side, beneath 
or behind the eye, as at f, fig. 1, Pl. XXIII. It is not provided with a valve. 
This condition of the funnel, together with the tegumentary protective covering of 
the eyeball, has relation to the more frequent emergence of the animal from its 
proper watery element, and its continuance in some recess on shore during low water. 
The colour of a Tritareopus so observed, and undisturbed, isa dullish pink, reflecting 
from parts of the “crown” a subviolet tint. But when irritated and alarmed it 
rapidly assumes tints varying from bluish ted to deep violet. ‘The inner surface 
of the coronal membrane, a, a, is of a lighter tint. The inner circular lip (fig. 2) is 
whitish. 
The mandibles have the usual deep-brown horny texture, the ventral one overlapping 
the narrower and shorter upper one ; both are trenchant, curved, and pointed. 
The accessory series of suckers in Tritaveopus may be noted as a step toward the 
Decapods, more especially the family Sepiadw, in species of which the suckers are 
crowded into three or more rows on a greater or less extent of the ordinary arms, or on 
the peduncles or accessory pair®. A reciprocal approach to the Octopodal type is indi- 
cated by another brachial character, exemplified in the species next to be described. 
1 «Tectures on the Anatomy of Invertebrates,’ 8yo, 2nd ed., 1855, p. 611, fig. 222. 
2 Tn a few species, Octopus fontanianus, d’Orb., e. g., three or four suckers on certain arms form a cluster 
much larger than the ordinary serial pairs. 
9 In Oranchia, as in Loliginide, the suckers are in two series on the ordinary arms (Trans. Zool. Soe. vol. ii. 
p- 107, pl. xxi. fig. 4). 
zZ2 
