Boone, Mollusca, Cruises of "Ara" and "Alva" 353 



conical, attached for about 6.5 of its len^h, with a W-shaped fun- 

 nel organ. The pallial septum is short, being equivalent to nearly 

 0.2 of the mantle length. The web is usually shallow, not exceed- 

 ing 0.15 of the arm length, of variable shape, the dorsal and next 

 to dorsal paired sectors being shallowest, while the remaining 

 sectors are deeper and approximately subequal. The arms are 

 quite long, being 0.80 to 0.85 of the total length, with the fourth 

 or ventral pair regularly the longest, the series usually decreasing 

 in the order 4, 3, 2, 1, but in some instances being 3, 4, 2, 1. The 

 suckers are moderately large and not crowded. The hectocotylized 

 arm is nearly a third shorter than its companion. The ligula is 

 small, about 0.4 of the related arm length, tapered, with a narrow, 

 deep, longitudinal ligular groove and a decided transverse, 

 obliquely curved groove proximal to the calamus. 



Colour: This octopus is a most unfortunate victim of M. 

 d'Orbigny's inappropriate specific name; when seen in its own 

 environment, the tropic shallows of the Red Sea and adjacent 

 regions, this graceful, gaily coloured creature has a unique, eerie, 

 gnomish beauty, as it glides among the rock crevices. It has a very 

 distinctive colour pattern, usually being of a reddish-magenta- 

 purple ground colour, reticulated with large circular to oval white 

 spots, in the center of each of which the octopus may erect a 

 cirrhus ; if attacked, or if seeking to frighten prey, waves of colour, 

 like blushes, pass over the body, so that the ground colour is thus 

 deepened and lighter tones of reddish-purple transiently tint the 

 creamy spots. 



References: Octopus horridu^, d'Orbigny, A., et Ferussac, A., 

 DE, Tabl. Meth. de la Classe des Cephal., Ann. Sci. Nat. ser. I, t. 

 VII, 1826, p. 144. — AUDOUIN, J. V., et Savigny, J., Descripte 

 de Egypte, etc.. Hist. Nat., 1826, 1. 1, p. 10, pi. 1, fig. 2.— RoB- 

 SON, G. C, Monogr. Recent Cephalop. Brit. Mus. Coll., pt. I, 

 1929, p. 91, text figs. 18-19 (with full synonymy) . 



