MACRUKOUS DECAPODA OF THE SUDANESE RED SEA. 377 



antennular peduncle, while the antennal scale reaches to the level of the 

 distal end of the second joint of the antennular peduncle. The lateral spine 

 of the basicerite is very acute and as long as the first joint of the antennular 

 peduncle, therefore slightly shorter than the stylocerite. The spine at the 

 upper angle of the basicerite is well developed, acute, about one-third as 

 long as the lateral spine. 



The telson (PI. 28. fig. 5) is two and a third times as long as wide at the 

 posterior margin. Its posterior angles are acute but not spinous, and 

 immediately inside of them the posterior margin bears two spines on each 

 side, the inner of which is slightly the longer. The usual two pairs of 

 dorsal spines are present, rather robust in form, the posterior pair situated 

 about the middle of the telson. 



The larger cheliped (PI. 28. fig. 2) is of the general form found in 

 S. biunguiculatas. The merus is triangular in cross-section, each angle of 

 the triangle marking a carina running longitudinally down the joint and 

 ending distally in acute spines. The carpus is acutely spinous at its lower 

 distal corner. Tbe ehela is rather more than 2i times as long as broad, quite 

 smooth and oval in form. The anterior margin of the palm ends in an acute 

 but not spinous tubercle. The fingers are about one quarter of the length of 

 the whole chela. 



The merus of the smaller cheliped is three times as long as wide, unarmed 

 at the apex, with numerous long seta? on the inner margin. The whole 

 chela is three times as long as broad, the palm being two-thirds of the total 

 length and the fingers one-third. The movable finger is tapering and 

 furnished with stiff sete at its tip. 



The merus of the second pair of legs (PI. 28. fig. 3) is very nearly five 

 times as long as wide. The carpus is about equal in length to the merus, 

 the first joint equal in length to the succeeding four, the last joint longer 

 than the combined length of the third and fourth. The chela is very 

 slightly shorter than the first joint of the earpus, with the fingers one and a 

 half times as long as the palm and fringed with long tufts of seta:'. 



The third pair of legs (PI. 28. fig. 4) are of relatively stout form. The 

 merus is rather more than three times as long as broad and unarmed. 

 The carpus is four-ninths; and the propodus two-thirds as long as the merus, 

 the carpus being unarmed and the propodus bearing seven short spines on 

 its inner margin. The dactylus is very short with the secondary nail well 

 developed. Length of the only male 13 mm., of the female 13-20 mm., the 

 smallest as well as the largest of which are oviuerous. 



This species falls within that group of forms belonging to the hiungiiicu- 

 latus division of the genus, in which the posterior margin of the sixth 

 abdominal somite is armed with teeth. De Man has described six species 

 in the Siboga Report, belonging to this group : S bispinosus, S. triacantkiis, 



JJNX, JOUIIN. — ZOOLOGY, VOL. XX.XIV. %9 



