214 WALTER GARSTANG. 



explanation of the wonderful exactitude with which the che- 

 lipeds fit the carapace, nor of certain peculiar relations M'hich 

 they bear to the respiratory channels to be now described. 



It is well known that in most, if not in all, of the Oxy- 

 stome crabs, the exhalant orifice of the respiratory canal is 

 carried to the tip of the snout by a prolongation of the endo- 

 podites of the first maxillipeds, either alone as in Calappa 

 (fig. 1, a, h), or with the co-operation of the endopodites of the 

 third maxillipeds, as in Matuta (fig. 2, a, b). 



The inhalant orifice has been shown, on the other hand, by 

 Milne-Edwards to vary considerably in position in the same 

 group of crabs. In most forms it is situated at the base of 

 the chelipeds, between these appendages and the adjacent edge 

 of the branchiostegite ; but in Dorippe,^ as already shown by 

 Milne-Edwards (1834, i, p. 89), it is situated further forwards, 

 and has the form of a deep emargination of the edge of the 

 pterygostomial portion of the branchiostegite. In Ebalia 

 and the Leucosiidse in general, the inhalant apertures occupy 

 a position which has hitherto been regarded as unique, being 

 situated beneath the orbits on the outer sides of the exhalant 

 orifice. They lead into a pair of deep aflFerent gutters exca- 

 vated in the external wall of the pterygostomial ^ plates. The 

 gutters are converted into closed canals by opercular expan- 

 sions of the exopodites of the third maxillipeds. In the 



' Examination of a specimen of this crab lias convinced me that in this 

 form also the chelipeds furnish an operculum for the peculiar afferent orifice, 

 but in a way quite different from that described below for Calappa and 

 Matuta. 



2 Not in the prelabial plate, as stated by Milne-Edwards (1839, p. 135) 

 and Dana (1852, p. 62). The language used by tlie former naturalist is 

 somewhat vague, but Dana at any rate has completely misinterpreted the 

 relations of the afferent gutter to the carapace in this family. I may here 

 draw attention to the fact that in the crab Myctiris platycheles of 

 Australian seas, the edge of the pterygostomial plate also exhibits a deep 

 gutter, which extends from the infra-orbital region to the afferent aperture at 

 the base of the cheliped, and thus closely resembles the afferent canal of the 

 Leucosiidse. The gutter is clearly subservient to the respiratory function, 

 and interesting results will undoubtedly reward the first careful investigator 

 of the respiratory processes in this aberrant representative of the Catometopa. 



