NO. 8 HAIG: THE ATLANTIC GALATHEIDEA 17 



PETROLISTHES Stimpson, 1858 



Key to the Western North Atlantic Species 

 (Based on Schmitt, 1935) 



1. Carpus of chelipeds entire 2 



Carpus toothed on anterior margin 3 



2. Front without a distinct lobiform tooth at inner orbital angles ; 



distal extremity of posterior margin of carpus ending in a 

 blunt angle or low obtuse tooth . . . quadratus 

 Front with a distinct lobiform tooth at inner orbital angles; 

 distal extremity of posterior margin of carpus ending in a 

 sharp spine tridentatus 



3. Lateral wall of carapace entire ; front not with 3 equally pro- 



jecting teeth; telson of abdomen with 7 plates ... 4 

 Lateral wall of carapace finely broken into pieces ; front with 3 



equally projecting teeth; telson of abdomen with 5 plates 9 



4. Carpus of chelipeds armed with 3 low, wide-set, spine-tipped 



teeth 5 



Carpus armed with 4 teeth or spines 6 



5. Carapace transversely rugose ; epibranchial spine present 



armatus 



Surface of carapace more or less smooth, not rugose; no epi- 

 branchial spine politus 



6. Carpus armed with 4 projecting spines; lateral margins of 



carapace armed with a row of small spines; margin of 

 front spinuliferous ; carapace rugose . . tortugensis 

 Carpus armed with 4 teeth or lobes; no spines (except epi- 

 branchial spine) on lateral margins of carapace ... 7 



7. Carapace very rough with prominent, transverse piliferous 



rugae galathinus 



Carapace more or less smooth, without prominent rugae . 8 



8. Front triangularly produced, its margin spinuliferous ; margins 



of chelae spinuliferous ; carapace not pubescent . amoenus 

 Front with a median, produced lobe, its margin not spinulifer- 

 ous; carapace pubescent marginatus 



9. Orbital margin straight, shallow, oblique; front greatly pro- 



duced; walking legs not hairy • . . vanderhorsti 



Orbital margin deeply concave; front not greatly produced; 



walking legs hairy nodosus 



