rg22.J S.Kemp: Notes on Crustacea Decapoda. 279 



Genus Conchodytes Peters. 



191 7. Conchodytes, Borradaile, Trans. Linn. Soc. (2) Zool. XVII, p. 

 392- 

 The species of this genus live, probably without exception, in 

 the mantle cavity of lamellibranch molluscs. In the possession 

 of a basal protuberance on the dactyli of the last three legs they 

 resemble Coralliocaris , but the}' are easily distinguished by a num- 

 ber of well-marked characters. The rostrum is depressed and 

 toothless, without a dorsal carina. The lower angle of the orbit is 

 produced, but neither antennal nor hepatic spines occur on the 

 carapace. The inner lobe of the maxillula is very broad and the 

 distal endite of the maxilla is broad and furnished with setae along 

 the whole length of its inner margin. The dactylus of the last 

 three pairs of legs is provided with two curved claws and the basal 

 protuberance is flat, not swollen and hoof-shaped as in Corallio- 

 caris. 



Borradaile recognises five species of this genus, but one of 

 them, C. margarita (Smith), 1 belongs in my opinion to the genus 

 Pontonia, in which it was originally described. Pontonia nippo- 

 nensis, which Parisi has recently shown to be a true Conchodytes, 

 must be added to the genus. If my identification is correct C. 

 biunguiculatus is represented in the collection I have examined. 

 This species was described by Paulson from an abnormal specimen 

 in 1875 and has not since been rediscovered. 



The host of C. nipponensis is unknown ; C. biunguiculatus lives 

 in Pinna, while, C. iridacnae and C. meleagrinae are usually associ- 

 ated with the genera of molluscs to which their specific names 

 refer. All the species are closely related to one another and it is 

 difficult to find valid characters for their separation. This is especi- 

 ally true of C. Iridacnae and C. meleagrinae which are perhaps not 

 specifically distinct. The former is apparently restricted to Tridac- 

 na : the latter is generally found in Meleagrina but according to 

 Borradaile sometimes also occurs in Triddcna. 



The four Indo-Pacific species may be separated by the follow- 

 ing characters : — 



A. Basal process of dactylus of last three legs with a 



small tooth on proximal side ; posterior of the two 



pairs of spines on back of telson situated about mid- . 



way between first pair and apex. 



B. Antepenultimate segment of third maxilliped less 

 than twice as Ion? as broad ; fixed nnger of second 

 leg with foremost tooth very broad and low, occupy- 

 ing greater part of distal half ; lateral spines of telson 



tip situated at apex ... ... ... biunguiculatus (Paul- 



son). 



B'. Antepenultimate segment of third maxilliped rather 

 more than twice as long as broad , fixed finger of 

 second leg with foremost tooth small and triangular ; 

 lateral spines of telson tip shifted forwards on to dor- 

 sal surface, not nearly reaching apex ... ... nipponensis (de Haan). 



1 See Addendum, p. 287. 



