26 THE VOYAGE OF H.M.S. CHALLENGER. 



RANINIDEA. 



Raniniens, Milne-Edwards, Hist. Nat. des Crust, t. ii. p. 190, 1837. 



Maninoidea, De Haan, Crust. Japon., p. 136, 1850. 



Raninidea, Dana, U.S. Explor. Exped., vol. xiii., Crust., part i. p. 400, 1852. 



Carapace ovato-oblong, smooth, the regions not defined ; frontal margin of variable 

 width. Ambulatory limbs with broad flattened dactyli ; the last pair of small size and 

 subdorsal in position. Abdomen short, semi-extended, not folded under the thorax, with 

 four pairs of appendages in the female. Sterna of the thoracic legs fused to form a 

 ventral shield which is wide anteriorly. External maxillipedes moderately elongate. 

 Eyes placed in well-marked orbits ; antennules not furnished with special fossse, 

 and placed to a certain extent behind the antennae. Vasa deferentia protruded 

 in the males. 



There can be no doubt that the Raninidea have many characters in common with the 

 Brachyura, indeed Dr. Boas places them without any hesitation in the latter section. 

 According to this observer, the position of the female genital openings is entirelj' 

 due to the extreme narrowing of the thoracic sterna which has taken place. In many 

 of their external features they show a decided resemblance to the Oxystomatous 

 Brachyura. 



The members of this small and distinct group form a single family. Little appears 

 to be known as to their habits, but according to Adams and White they are swimming 

 Crustacea inhabiting deep pools of coral ledges, and moving by rapid jerks like the 

 Galathese. It seems probable, however, that some of them at least burrow in sand or 

 mud like the Hippidea, to which they bear some resemblance in the structure of the legs. 

 They are almost entirely confined to the tropics, only a few occurring in the warmer 

 temperate seas, wdiere they live in shallow and moderately deep water, apparently not 

 venturing beyond a depth of 300 fathoms. 



The genera may be grouped as follows : — 



1. External maxillipedes with the ischium longer than the merus — ■ 



Ranina, Lamarck. 

 Raninoides, M.-Edw. 

 Notopus, De Haan. 



Noto'poide.s, n. gen. 



Zanclifer, n. gen. 



Cosvionotiis, Adams and White (?). 



Raninops, A. M.-Edw. (1). 

 II. External maxillipedes with the ischium shorter than the merus. 

 Ranilia, M.-Edw. | Lyreidus, De Haan. 



