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Show '280 SIR C. ELIOT ON NUDIBRANCHS [N o v . 2 9 , Phyllidiopsis and CeratophylUdia the mouth-parts are much as in Doridopsis, the glands not being fused with the buccal tube, and Ceratophyllidia has the additional peculiarity of bearing stalked globes on the back. The distinction between Phyllidia and Phyllidiella seems to me less certain. According to Bergh, (a) the oral tube is symmetrical in Phyllidia, asymmetrical in Phyllidiella; but I have not found the difference to be clear or persistent, and even if it is so, I doubt if it is of generic worth. (b) In Phyllidia, " Dorsum tuberculis elongatis, plus minusve con-fluentibus obsitum, medio varicositates longitudinales formant-ibus." In Phyllidiella, " Dorsum proprium tuberculis discretis vel pro parte confluentibus quincunces formantibus obsitum." Even in typical forms it does not appear that this distinction is clear. Phyllidia elegans (see Bergh's Monograph, pi. xix. fig. 1) seems to me to have not " varicositates longitudinales," but groups of confluent tubercles; and, on the other hand, Phyllidiella pustulosa strikes me as having not so much tubercles arranged in " quincunces," as compound tubercles arranged in lines. But in abnormal forms, which are frequent, it is still harder to draw the distinction. I have a fine specimen with all the characters of Phyllidia varicosa, but the median ridges, though very distinct posteriorly, are broken up in front and unite to form a quincunx as in Phyllidiella nobilis. Again, in this latter, the quincunces are often placed so regularly above one another that the tubercles seem to be arranged in longitudinal lines and not in figures. I therefore think it better to abandon Phyllidiella as a separate genus. The arrangement of the dorsal tubercles in these forms is so variable, that it is hard to draw the line between species and varieties, but at least three certainly specific forms occur in East Africa:- (1) Ph. varicosa.-Colour black, blue, and orange ; rhinophores yellow. A black stripe on the foot. Tubercles more or less fused into ridges, but not compound. Typically, there are three long ridges down the centre of the back and a number of short ridges, more or less at right angles to them, running inwards from the mantle-edge. Buccal mass yellow and very complicated. (2) Ph. pustulosa.-Black and green; rhinophores black, no black line on foot. Tubercles simple or composed of only two or three lumps. Buccal bulb partly black. ' ,(3) Ph. nobilis.-Colour as in Ph. 'pustulosa, but tubercles highly compound, sometimes consisting of ten small lumps fused together. Typically, they are arranged in square or oblong figure Buccal bulb large, yellow. That the patterns formed by the tubercles should vary is not surprising, if we consider that the tubercles have always a tendency to unite, and may do so more or less decidedly in a given direction. Thus the typical form of Ph. varicosa occurs when the lateral tubercles unite in a predominantly transverse direction. When however, union in a longitudinal direction |