19^9-1 S. Kp:mp : Notes on Crustacea Decapoda. 347 



by Miss Rathbun is from a mangrove swamp at Lem Ngob in the 

 Gulf of vSiam. 



Tympanomcrus orientalis (de Man). 



1888. Dioxippe oi'ientalis. de Man. 'Jonr/i. f.iiin. Soc. Zool.. XXI I. ]>. i v"^. 



pi. ix, figs. 8-10. 

 iQiio. Tvnip/ii/oments orientalis. Alcock, Jouvii. Astai. Soc. Beiio,,/ I.XFX, 



P- 371. 



^Li^ .Mergui Archipdago. iMus. C:ollr. Seven. P\K\rwF.s. 



Not known from any other localit}'. 



Tympanomcrus gangeticus, sp. nov. 

 Plate XIII, tig. 3. 



This species, which is represented only by two specimens one 

 of which is imperfect, is very closely allied to de Man's Tympano- 

 merns orientalis, resembling that species in the possession of a 

 strong tooth on the inner face of the carpus of the chelipedes. 



T. gangeticus differs from T. orientalis in only two conspicuous 

 features : — (i) the lower border of the orbit shows no trace of the 

 large obtuse lobe found near the outer end in de Man's species ; 

 (ii) the crest defining the lateral borders of the upper surface of 

 the carapace is regularly convex behind the small anterior ex- 

 cavation, the upper surface 

 being widest in front of the 

 middle point. In T. orien- 

 talis the crest takes a sinu- 

 ous course ; it is distinctly 

 concave anteriorly and is 

 obtusely angled behind the 



middle, ^ the upper surface y^^.y,,^, ^o.-Tvmpanomerus ^rangeficus. 



being widest at this point. sp. nov. 



In other respects the dif- Chela of male, 



ferences are small The 



front is a httle broader, with its lateral angles more broadly 

 rounded and its sides more oblique ; its apex does not possess a 

 median point. The median groove on the upper surface is deeper 

 and the front when viewed from above is more conspicuously 

 emarginate distally There are numerous scattered setae on the 

 lateral parts of the upper surface of the carapace. The buccal 

 cavern is broader and the merus of the external maxillipeds is 

 as broad as long (in T. orientalis it is longer than broad). The 

 surface of the merus bears numerous very ^hoxt setae. 



The chelipeds are a little shorter : the length of the chela is 

 considerably less than the anterior breadth of the carapace. The 

 upper surface of the carpus is finely roughened and bears numerous 

 minute granules antero-externally. The walking legs are a little 

 shorter and stouter ; the merus of the penultimate pair is less than 

 two and three quarter times as long as wide, whereas in specimens 



