ISOMETBUS. 4f> 



spine or vesicle beneath the aculeus. Immovable finger of mandible 

 armed beneath with 1 tooth. Finger of chela armed with only 

 about five or six median rows of teeth set end to end without 

 overlapping, also with an inner series consisting of six large 

 teeth set close to the apices of the median rows, and an outer 

 series of large teeth corresponding to those of the inner series, 

 and placed in a straight transverse line with them. Protarsal 

 segments of legs cylindrical, sparsely and irregularly hairy. 



Type, 1. europceus, Linn. 



Distribution. Oriental Eegion, from India as far east as Queens- 

 land. (The typical species, /. europceus, has been transported all 

 over the tropics and even to Europe in connection with shipping.) 



Synopsis of Indian Species. 



a. Posterior surface of brachium rounded, without 



crests ; 5th caudal segment wide and high . . /. rigictulus, p. 52. 



b. Posterior surface of brachium distinctly ciri- 



nate ; 5th caudal segment low and narrow. 

 a 1 . Aculeus short, not more than half the 

 length of the vesicle; tarsi furnished 

 witli two rows of bristles ; pectinal teeth 

 12-16. 



a~. Dorsal keels of 2nd and 3rd caudal seg- 

 ments armed posteriorly with an up- 

 standing spine; pectinal teeth 16 /. acanthurus, p. 51. 



b~. Dorsal keels of caudal segments not fur- 

 nished with posterior upstanding spine ; 

 pectinal teeth 12-14. 



a 3 . Vesicular spine acutely angular; dorsal 

 surface of abdomen ornamented with 

 a pair of complete longitudinal pale 



bands /. vittatus, p. 50. 



b 3 . Vesicular spine with rounded apex : 

 dorsal surface of abdomen not orna- 

 mented with two complete longi- 

 tudinal yellow bands. 

 4 . Colour black, variegated with yel- 

 low ; tail and hand thinner /. brachycentrus, 



b 1 . Colour yellow, variegated with black; [p. 5C 



tail and hand thicker /. bastticus, p. 49. 



b 1 . Aculeus long, nearly as long as vesicle; 



tarsi thickly hairy beneath. 

 a 5 . Superior keels *of 2nd and 3rd caudal 

 segments ending in an acute upstanding 

 spine ; last abdominal sternum with 



only a pair of crests /. assmnensis, p. 48. 



b. Superior keels of 2nd and 3rd caudal 

 segments not spined ; last abdominal 

 sternum with four crests. 

 a 6 . Pectines in furnished at base with 



rounded expansion above first tooth. . /. ttiwaitesi, p 48. 

 b 6 . Pectines in without lobate basal 



expansion. 

 a~. Pectinal teeth 15-16; ante-ocular 



