182 PROF. OWEN ON NEW AND RARE CEPHALOPODA. 
pretty closely resembling, in average size and in the extent of the basal interbrachial 
membrane, the common Poulpe (Octopus vulgaris) of our own shores. As, however, the 
acetabular character seems to be of equal distinctive value to that of the opposite extreme 
connotive of Eledune', I regard the present species as the type of a genus, the character 
of which has suggested the name above given. 
The following are dimensions of my specimen of Tritaxeopus :— in. lin. 
Length of the body. . . . aor yw 
5, of the head to the hivinion of the ded nace of the arms. . 2 O 
», of the animal to the free margin of the interbrachial web . 8 O 
Bréadthi of body mt tits hinder balf:,. .....5) %) «ele os) Pode by one ee 
ee of head, acrossthe eyes . . ; 2 3 
The arms differ as to length in the order daracenaee of ihe aaepid sautiog of the 
* Poulpes” in D’Orbigny’s monograph *, and graduate in the special manner seen in 
Octopus vulgaris: viz., the “third” arm counting from the dorsal (1) to the ventral (4) pair, 
being the longest, the “second” arm is but little longer than the “fourth,” and the “first” 
is the shortest. The length of the “ third” arm in the specimen figured (Pl. XXIII. 3) 
is 1 foot 11 inches, that of the first (ib. 1) being 1 foot 2 inches. The basal thickness 
of the fleshy part of the third arm is | inch; and this dimension does not diminish in the 
same degree as does the length in the shorterarms. The extent of the basal webs, a, a, 
uniting the arms from the base to the middle of the free margin, is 25 inches between 
the second (2) and third (3) arms, and 13 inch between the first (1) and second (2) 
arms. The proportional magnitude of the ‘“‘ cephalic crown,” formed by the arms and 
their webs, to the body, in Tritaxeopus cornutus, is as great as in Octopus vulgaris *. 
The integument of the body is beset with scattered wart-like prominences, chiefly on 
the dorsal aspect; and, of these, four or five of the largest affect a longitudinal 
disposition. 
The tegumentary eyelids are well developed; and each supports prominences on the 
upper border, of which the two anterior are so large and pointed as to simulate horns, 
whence the nomen triviale of the present species. 
The fleshy stem or basis of the arms is, in transverse section, rather semicircular 
than trihedral. The flat side supports the suckers. They begin at the brachial 
basis (ib. fig. 2) in a single series, and, alternating in position after the third or 
fourth, assume the ordinary biserial arrangement; then the two series diverge after 
‘ Dr. Gray, in the ‘Catalogue of the Mollusca in the Collection of the British Museum,’ Part i. (12mo, 1849) 
—CrrHaLoropA anTEPEDIA—defines the genera Octopus, Cistopus, Pinnoctopus, as haying “ arms with two rows 
of cups” (p. 4), in contradistinction from Hledona and Cirroteuthis, which have “‘ arms with one row of cups.” 
2 « B. Bras latéraux les plus longs” (Histoire naturelle générale et particuli¢re des Céphalopodes Acctabu- 
liféres,’ &e., fol. 1839, p. 17). 
* M. dOrbigny remarks on this character of “la couronne :’—‘ Son volume extraordinaire distingue de 
suite l’Octopus vulgaris des autres esptces ” (op. cit. p. 28). It applies, however, more precisely, to the female 
of the species ; and the subject of Pl. XXIII. fig. 1 of the present memoir is of this sex. 
