1904.] FROM EAST AFRICA AXD ZANZIBAR. 93 



than visual in the other species, but with a very thick rhachivS and 

 bipinnate. The rhinophores are large and exserted, each bearing 

 about 35 perfoliations. The rims of the pockets are very slightly 

 i-aised. The oral tentacles are two hard black ridges, curved 

 downwards and sideways. The foot is narrow and grooved in 

 front. 



The buccal mass was extracted, but the animal was not further 

 dissected in order to preserve the specimen. There is no labial 

 armature. The formula of the radula is 13 X 3-t-l-l.l + 3. The 

 teeth closely resemble those of iV. gratiosa, the chief difference 

 being that the anterior margin of the wide median tooth (fig. 3 c) 

 is indistinctly bilobed, the right half being always a little higher 

 than the left. The first lateral (fig. 3 d) is large, rather irregular 

 in shape, and with a double hook at the apex. 



This form is closely allied to iV. gratiosa, and were the latter 

 found in the Indo- Pacific region, I should be inclined to regard 

 them as varieties of one species. But A\ gratiosa is recorded from 

 the West Coast of Mexico *, which lies outside of the Indo- 

 Pacific area ; and it is therefore probable that the differences pre- 

 sented by the present animal are real and greater in living indi- 

 viduals, {a) It is not mentioned that N. gratiosa is remarkably 

 soft, {h) The present specimen shows no traces of ridges near 

 the rhinophores or on the tail, (c) The coloi'ation of N. gratiosa 

 is not dissimilar, but the pattei'n is spotted whereas here it is 

 striped, {d) The tentacles do not look as if they had ever been 

 ear-shaped. (e) Tlie antei'ior margin of the median tooth is 

 indistinctly bilobed. 



Marionia. 



[See especially Bergh, in Semper's Reisen, xv. p. 737, &, xvii. 

 p. 890.] 



All the Tritoniadse which I have collected in East Africa belong 

 to this genus, unless the form described as Marionia sp. is regarded 

 as sufficiently certain to constitute a new generic type. Marionia 

 is distinguished from its near allies Trit07iia and Candiella by the 

 presence of a circle of horny plates or leaves in the stomach. The 

 velum bears distinct processes, which are often ramified. The edge 

 of the jaAV has one or more rows of denticles, and the radula is 

 moderately wide. The central tooth is broad and more or less 

 distinctly tricuspid. The latei'als are hamate, but the first one is 

 larger and clumsier than the others. Provisionally I think it 

 best to divide the forms here described among six species, but am 

 by no means certain that they will all prove valid. When more 

 material can be examined it will probably be found that the 

 species of Marionia exhibit many varieties in foi^m and colour and 

 run one into another. It is also not impossible that the denticu- 



* In Bergh's ' System der Nudibr. Gasteropoden,' p. 1145, the locality is given as 

 " mare indicum, Amboina," but this appears to be a slip. The animal is described by 

 Bero-h araon^ the molluscs of Amboina, but is expressly said to come from Mexico. 



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