1903.] FROM EAST AFRICA AXD ZANZIBAR, 385 



most are set almost at right angles to the rhachis. The stomach 

 is large and free, but thin and not laminated nor muscular. The 

 blood-gland is large, and the nervous system is very concentrated. 

 The generative system appears to be as described by Bergh, but 

 the glandula and hasta amatoria are difficult to see and were 

 satisfactorily detected only in one specimen. 



These specimens are, I think, clearly Ehrenberg's Asteronotus 

 hemprichi, from Massaua. He describes it as " sex-poUicaris, 

 oblongus, glaber, vesiculosus, supra fuscus, lineis circulisque niveis 

 sparsis, vesicas dorsuales cingentibus, subtus lateritus, pede flavido, 

 branchiarum apertura lobulis sex stellatim positis prsecludenda. 

 .... Branchiarum e dilute laterito seu carneo albicantium 

 fasciculus amplus." 



Prof. Bergh seems inclined to think (S. R. xvii. p. 917) that 

 the real species of this genus are not moi'e than three, hemprichi, 

 mabilla, and ccespitosus. The differences between these three 

 do not seem to me to be clearly defined, and my numei'ous 

 specimens, which I unhesitatingly refer to one species, present 

 connecting links, especially in colour, which make me think that 

 the three species are merely varieties of one. 



EXPLANATION OF THE TLATES. 

 N.B.— Except in the cases noted, the figures are drawn from the living animal. 



Plate XXXII. 

 Fig. 1. Thordisa villosa (p. 367), ventral view. 



2. Dorsal view of the same. 



3. Thordisa crosslandi (p. 368), ventral view. The margin of the mantle is 



inturned here and there, showing the mobile papillae which cover the 

 dorsal surface. 



4. Trippa monsoni (p. 371), dorsal view, much enlarged. 



5. Salgerda willeyi (p. 372), from a drawing by Dr. Arthur Willey. 



Plate XXXI 1 1. 

 Fig. 1. Thordisa villosa (p. 367), head and anterior end. The figure shows an 

 extreme elevation of the body, which normally is Hat. 



2. Dorsal papilla of the same species, with flexible pigmented end and spicule- 



stifl^ened base. Also a portion of the mantle-edge magnifiied. 



3. Branchiae of the same. 



4. Thordisa crosslandi (p. 368). Teeth from the radula : a, upstanding ; 



b, laid flat. 



5. Gills and anus of the same. A ridge (a) connects the higher part of the 



rhachis with the anal papilla {/>). 



6. Dissection of the retracted penis ot the same, showing the shape and structure 



of the enclosed glans. 



7. The glans penis of the same is slit open, showing it to be hollow and to 



contain a prolongation of the vas deferens which passes to its tip. 



8. The central nervous system of the same in its sheathing of connective tissue. 



Platk XXXIV. 

 Fig. 1. Halgerda wnsinensis* (p. 373), dorsal view. 



2. Diagram of the arrangement of its gill on the rhachis. 



3. Sclerodoris coriacea (p. 383). Pencil drawing from the preserved speeiinen. 



4. Degenerate Copepod parasite found in the liver of Sclerodoris (p. 384). 



5. Asteronotus hemprichi (p. 384). 



6. Enlarged view of the gill-opening when the branchiae are as completely 



retracted as is possible. 



7. K.entrodoris rubescens (p. 374), about half natural size. 



* This name is wrongly spelt " wassinensis " on Plate. 



rKoc. ZooL. Soc— 1903, Vol. II. No. XXY. 25 



[33] 



