140 A HISTORY OF RECENT CRUSTACEA 



SO, thougli sucli a species as Petalomera pulchra in the pre- 

 ceding legion does not seem to suit the theory. One may, 

 however, suppose that in some instances a re-widening of 

 the plastron may have been developed without any re- 

 arrangement as to the position of the vulvge. 



This legion contains the single family Raninidee, for 

 which, therefore, no separate character is needed. It 

 includes some nine genera, limited to the warm seas, and 

 inhabiting chiefly the tropics, with a range of depth 

 ajDparently not exceeding 300 fathoms. 



Ranina scahra (Fabricius), originally called Cancer 

 ranimis, Linn., and afterwards Banina serrata, Lamarck, 

 and Ranina dentata, Latreille, from Amboina and the Sand- 

 wich Islands, was known to fame long before a separate 

 genus was established for it. The carapace has been com- 

 pared to an inverted triangle. It is very broad anteriorly, but 

 the sides slope very gradually to the rounded hinder margin. 

 The eye-stalks are three-jointed, strongly geniculate, and 

 have a very deep orbit. The pterygostomian regions of the 

 carapace unite with the sternal plastron so as completely 

 to separate the third maxillipeds from the chelipeds. The 

 plastron itself is anteriorly almost trefoil-shaped, but to 

 the rear becomes linear. The branclii^, Milne-Edwards 

 says, are arranged as in the Brachyura, but in the confor- 

 mation of the respiratory cavity there is a peculiarity of 

 which he knew no other example. As in the Leucosiidse, 

 the carapace is joined to the sternum and the cavity of the 

 sides, without leaving above the base of the feet or maxil- 

 lipeds any space for the entrance of the water necessary 

 for breathing, but the afferent channel instead of being 

 pierced beside the efferent channel, on the sides of the 

 mouth, is situated behind and has a special opening below 

 the base of the pleoii. This view, however, is criticised by 

 de Haan in a passage that is not free from perplexity. 

 ' In Portunus and Grapsus,' he says, ' the water is brought 

 to the branchise by a double path and removed by a double 

 path ; it reaches the branchial cavity by the mouth and 

 the apertures near the base of the chelipeds ; but it passes 

 out both by the space between the inferior lateral margin 



