1904.] erom east africa and zanzibar. 401 



Ceratosoma cornigerum*. 



[Bergh, Semper's Reisen, x. pp. 393 fF. ; id. ' Challenger ' Reports, 

 pt. xxvi. p. 80 ff.] 



ISTumerous .specimens of Ceratosoma, mostly found together and 

 apparently belonging to one species, were captured at Ohviaka in 

 February 1901. About 40 of them were preserved. 



The living animals varied greatly in coloration, the ground- 

 tint ranging from olive-green to deep chestnut-red, with grada- 

 tions in each shade. On this ground were numerous dark brown 

 spots and white mottlings in varying proportions, but it is to be 

 noted that the variations in the ground-colour were real and did 

 not depend on the markings. In all specimens there were a row 

 of violet dots round the foot, and violet lines or spots on the head 

 near the rhinophores, and generally near the branchife as well. 

 The ground-colour near the edge of the foot was white. One 

 specimen was dark green with orange-yellow spots, and in all 

 cases there were a few yellow spots neai' the edge of the foot and 

 the genital orifices. 



Many of the animals were found in shallow pools, crawling over 

 seaweed and in no way hiding themselves. They were sluggish 

 in their movements, and had a peculiar, unpleasant, strongly 

 aromatic odour. In many specimens the tail or the posterior 

 dorsal process appeared to have been bitten off. Possibly the 

 curious shape may really be a protection to the animal by enabling 

 it to escape with nothing worse than the loss of an unimportant 

 part when it is seized by a carnivorous foe. No instances of self- 

 mutilation were observed. 



The alcoholic specimens show considerable variation in size 

 and proportions. Some are stout, some slender with relatively 

 longer tails ; in some the lobes are much thicker than in others. 

 Note was taken of one living specimen which had no lobes at all ; 

 another had two lobes like horns near the rhinophores. It does 

 not appear that these variations in size and shape correspond 

 with any differences in the radula, branchiae, or other organs. 



The measurements of an average fine specimen are as follows : — 

 Total length 89 mm., tail 34 mm. ; extreme height to tip of pos- 

 terior lobe 33 mm., extreme breadth across lateral lobes 26 mm. 

 The posterior lobe rises 10 mm. above the level of the back, and 

 the lateral lobes project 6 mm. from the line of the sides. The 

 pockets of the rhinophores and branchiae have slightly raised 

 rims in some specimens, but not in all. The rhinophores are 

 rather large ; the club bears about 40 perforations on each side, 

 and is supported on a stalk about as large as itself. The branchiae 

 are long and string-like ; in nearly all the specimens they project 

 from the pocket and are not retracted. The arrangement is 



* In my paper on Mr. Gardiner's collection of Nudibrancliiata, in the ' Fauna and 

 Geography ot the Maldive and Laccadive Archipelagoes,' I inadvertently alluded 

 (p. 552) to Ceratosoma 2^oli/omma as common in East African waters. I should 

 have said C. cornigerum. 



