112 MR. OWEN'S DESCRIPTIONS OF 



of the head ; the greatest breadth of the body is 4 Imes ; the breadth of the head, in- 

 cluding the eyes, is half an inch. Of the eight arms which radiate from the anterior 

 part of the head, the first or dorsal pair is the longest, as is the case in many species 

 of Octopus ; the second pair is nearly the same length as the first ; the third pair, which 

 is commonly the longest in the Decapods, is here scarcely half the length of the first ; 

 the fourth pair is nearly two thirds the length of the first. 



The musculo-membranous web which is usually extended between the bases of all 

 the arms in the Octopi, is in this species developed to the ordinary extent between the 

 four dorsal arms only : the webs between the second and third, and the third and fourth 

 arms are very short ; that between the fourth pair is wanting. From this peculiarity I 

 propose to name the species Octopus semipalmatus. The suckers are sessile, and are 

 arranged in a double close-set alternate series on the margins of the internal surface of 

 the arms, with a broader interspace than is usually observed (figg. 12, 13. PI. XXI.) 



The eyes are of proportionally lai'ge size, and present a dark colour, in consequence 

 of the pigment shining through the sclerotic coat. The sclerotic is perforated by a cir- 

 cular aperture in the usual situation ; and as the dermal cornea, which covers the ante- 

 rior part of the sclerotica in the common Poulp, is absent in this species, the capsule of 

 the crystalline lens is exposed, as in the Nautilus, to the sea-water. The funnel has the 

 usual exterior form : it is without a valve ; but at the sides of its base there is a struc- 

 ture approaching to the articulation by which it is united to the mantle in the Decapo- 

 dous tribe of Cephalopods. Immediately above the insertion of each lateral pillar there 

 is a small transverse crescentic ridge which rests upon a similar ridge projecting from 

 the side of the mantle (see a, h, fig. 13. PL XXI.) ; neither of these prominences however 

 is supported by cartilage, as in the Decapoda. In the Octopus catenulatus there is a 

 similar structure, but the projection on the mantle is shorter and more prominent ; in 

 the Argonauta the articulation of the sides of the funnel is still more complete, and is 

 constant in all the known species of that genus'. 



With respect to the anatomy of this small Cephalopod it may be observed, that in 

 the presence of a crop, in the lateral insertion of the gullet into that receptacle, in the 

 muscular stomach, the spiral laminated bag, and the folded intestine, it accords with 

 the generic type of structure presented in the common Poulp {Octopus vulgaris, Cuv.). 

 The ink-bag is similarly buried m the anterior part of an undivided large liver : the biliary 

 ducts are without glandular appendages : the follicles appended to the branchial divisions 

 of the vena cava, are elongated, and hang from the exterior of the vessels ; the branchial 

 hearts are without fleshy appendages ; the branchics are connected by membranous 

 bands to the sides of the mantle ; the branchial lamince present a zig-zag folding, as in 



' The preceding examples of the infundibular joints in the genus Octopus diminish the value of that cha- 

 racter as distinguishing Ocythoii from Octopus. See Dr. Leach's account of Ocythoe Crane/5«', —Phil. 

 Trans. 1S17, p. 295. 



