's RIJKS MUSEUM VAN NATUURLIJKE HISTORIE — LEIDEN. 155 



17. Outer orbital angle sharp; a snort „musical crest" at the fore margin 

 of the arm of the male cheliped ; three obtuse tubercles in the outer 

 half of the under orbital border ; immobile finger with a large tooth 

 occupying nearly the whole distal half of the finger. M. quadratus. 



Outer orbital angle rectangular or somewhat sharp, in the latter 

 case not projecting farther than the antero-lateral tooth of the cara- 

 pace; no „musical crest" at the fore margin of the arm of the male 

 cheliped; immobile finger with or without larger tooth. 18. 



18. Immobile finger without larger tooth; a row of granules near the 

 under border of the palm. 19. 



Immobile finger with a large tooth, outer surface of palm smooth, 

 without a row of granules ; carapace subquadrate ; front occupying 

 one-third of the greatest width of the carapace ; outer orbital angle 

 not projecting farther outward than the antero-lateral tooth, both 

 teeth of nearly the same shape. M. punctulatus. 



19. Outer orbital angle rectangular; sides of the carapace convergent 

 posteriorly; immobile finger not deflexed, in the same line with the 

 lower border of the palm. M. setosus. 



Outer orbital angle somewhat pointed ; sides of the carapace arched ; 

 immobile finger deflexed, forming a curved line with the lower border 

 of the palm. M. latifrons. 



20. Carapace and legs very much hairy ; no longitudinal rows of gra- 

 nules on the posterior branchial regions. M. crinitus. 



Carapace with some scattered hairs, with larger or smaller gra- 

 nules, sometimes smooth ; on each branchial region two nearly 

 parallel rows of larger granules, among which are inserted very 

 short hairs, above the insertion of the last pair of legs runs a similar 

 but much shorter row, and finally there is a fourth row, that runs 

 transversely at the level of the last lateral tooth of the carapace. 21 . 



21. Carapace smooth, glossy; immobile finger of male cheliped with a 

 faint longitudinal rim, meropodites of last pair of walking legs with 

 a spine near the distal end. M. pacificus. 



Carapace granular ; meropodites of last pair of walking legs without 

 a spine near the distal end. 22. 



22. Carapace conspicuously narrowed anteriorly; a „musical crest" at 

 the fore margin of the arm of the male cheliped ; under margin 

 of the orbital groove in its outer fourth part formed by three round- 

 ed tubercles. M. tomentosus. 



Carapace less narrowed anteriorly ; no „musical crest" at the fore 

 margin of the arm of the male cheliped ; under margin of the orbital 

 groove not modified into obtuse tubercles but wholly crenulated. 23. 



