igiQ-] S. Kemp : Notes on Crustacea Decapoda. 307 



the abdomen are constricted as in the other sex. We have thus a 

 female possessing a male character that can hardl}' be called 

 secondary, for it can be demonstrated without difficulty that the 

 purpose of the constriction in the male abdomen is that of per- 

 mitting the copulatory appendages to remain exserted, while the 

 abdomen is folded against the carapace 



This paper was almost completed before I became acquainted 

 with Dr. Tesch's report on the Catometope crabs obtained b}^ the 

 ' Siboga' Expedition, published in 1918. In this report (pp. 40 et 

 seq.) will be found a summary of the characters of the genera and 

 species of the Scopimerinae and full descriptions of certain forms. 

 My own work thus to a great extent covers the same ground as 

 that traversed by Tesch, but there are considerable differences in 

 our treatment, and, apart from the new^ species I have to intro- 

 duce, an independent consideration of the subfamil^^ will, I believe, 

 have its uses. 



Tesch gives to the subfamily the name Mictyrinae and includes 

 in it Latreille's Mictyris, usually placed in a separate family. This 

 view is not supported by any discussion and, having examined 

 both the species belonging to Latreille's genus, I am unable to give 

 my adherence to it. 



Mictyris differs from the members of all other Catometope 

 families in a number of very important features. Apart from the 

 absence of defined orbits and the extraordinary disposition of the 

 third maxillipeds, the mouth-parts differ widely from those of all 

 genera of Oc5^podidae with which I am acquainted, while in the 

 possession of an unpaired accessory branchial orifice at the extreme 

 posterior end of the carapace the genus is unique among Decapoda.' 



1 In ne.irly all Brachyrhynchous crabs water is normally drawn into the 

 branchial chamber through an aperture at the base of the chelipeds and is ex- 

 pelled through the buccal cavern between the endostome and the distal ends of the 

 outer maxillipeds. In Mictyris and in certain Ocypodid genera, all of which 

 are amphibious in habit, accessory passages to the branchial cavity are to be found. 

 The external orifices of these passages are rendered conspicuous by reason of a 

 thick fringe of short hairs which doubtless serves to prevent the intrusion of 

 particles of sand. 



In Ocypoda and Gelnsimus the orifice of the passage takes the form of a 

 hairy-edged pouch situated between the bases of the 2nd and 3rd walking legs. 

 From this pouch a channel passes upwards to the branchial cavity either through 

 a gap between the upturned margins of the coxae (very conspicuous in O. 

 cevatophthabna) or through an aperture behind their fused edges. In Heloecitis 

 similar pouches exist between both the ist and 2nd and between the 2nd and 3rd 

 walking legs. Of Scopimerine genera Scopimeva possesses an accessory branchial 

 passage with the orifice placed between the bases of the ist and 2nd legs, and 

 similar passages also exist in certain species of Tympanomeriis, the orifices being 

 found between the bases of the ist and 2nd, 2nd and 3rd and (sometimes) the 3rd 

 and 4th walking legs. 



The unusual structure of the branchial opening at the base of the chelipeds 

 in Mictyris has been described by Alcock, who does not, however, refer to the 

 accessory passage also found in this genus. The orifice of this passage differs 

 from that of all the Ocypodid genera referred to above in being unpaired. It is 

 situated at the extreme hinder end of the animal and is bounded dorsally by the 

 short posterior margin of the carapace and ventrally by a strong transverse ridge 

 on the first abdominal segment, both upper and lower borders being heavily 



