PEOF. OWEN ON NEW AND EAEE 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, c); 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 /, fig. 1, PI. 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 Mater. 



The colom-of a Tritaxeopus so observed, and undisturbed, is a dullish pink, reflecting 

 from parts of the " crown " a subviolet tint. But when irritated and alarmed it 

 rapidly assumes tints varying from bluish red to deep ■\'iolet. 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 homy texture, the ventral one overlapping 

 the narrower and shorter upper one ; both are trenchant, carved, and pointed. 



The accessory series of suckers in Tntaxeojms may be noted as a step toward the 

 Decapods, more especially the family Sepiadm, 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 I A reciprocal approach to the Octopodal type is indi- 

 cated by another brachial character, exemplified in the species next to be described. 



' 'Lectures on the Anatomy of Invertebrates,' 8vo, 2nd ed., 1855, p. GU, fig. 222. 



' In a few species, Octoims fontaniamis, d'Orb., e. g., three or four suckers on certain arms form a cluster 

 much larger than the ordinary serial pairs. 



' In Cranchia, as in Loliginida;, the suckers are in two series on the ordinary arms (Trans. Zool. Soc. vol.ii. 

 p. 107, pi. xxi. fig. 4). 



z2 



