CRUSTACEA. 



273 





1 



Dana's description of his P. biunguiculatus *, in having a distinctly 

 trilobate front, the middle lobe of which is broad, subacute, or 

 rounded, and not much more prominent than the lateral lobes ; 

 whereas in P. biunguiculatus, to which species specimens from the 

 Gulf of Suez (B. Mac Andrew) appear to belong, the median lobe is 

 very prominent and acute and the Literal lobes obsolete. The spe- 

 cimens referred to P. biunguiculatus also differ from P. obesulus in 

 having the outer surface of the palms of the chelipedcs much more 

 close!}' punctulated. The ccphalothorax is narrowest in the smallest- 

 sized specimens ; and in the female from Port Denison (which is 

 one of the largest examples I have seen) is much broader than in 

 the others ; but I cannot regard this character by itself as of specific 

 importance. 



I am inclined to doubt whether the genus Polyonyx is distinct 

 from Megalobrachium. Stimpson merely distinguishes the latter 

 on account of the absence of the prominent accessory claw, which 

 gives to the dactvli of the species of Polyonyx a biunguiculate 

 appearance. The type of Megalobrachium (J/, granuliferum, Stm.) 

 is from the West Indies : but Stimpson refers the P. macrochelis, 

 Gibbes, from Carolina, to the genus Polyonyx. The other species of 

 the latter genus are Oriental in habitat. 



Specimens are referred to P. biunguiculatus by Mr. Haswell from 

 Holborn Island, Port Denison, by whom also this species is retained 

 in the genus Porcdlana (vide Cat. p. 147). 



17. Pachycheles pulchellus {Hasivell). (Plate XXX. fig. A.) 



Porcellana nulchella, Haswell, Proc. Linn. Soc. N. S. Wales, vi. p. 758 

 (1881) ; Cat. Austr. Crust, p. 148 (1882). 



As Mr. Haswelfs description is very brief, I append the following 

 from specimens received from Dr. Coppinger : — 



The carapace is smooth, rather convex, rounded on the sides, and 

 hence somewhat orbiculate in outline, faintly striated on the sides 

 at the back of the branchial regions. The front is rather broad, and 

 in a dorsal view its margin appears straight ; in an anterior view it 

 is seen to be bisinuated, with a broadly rounded but very slightly 

 prominent median lobe. The orbital and lateral margins of the 

 carapace are entire. The first exposed joint of the peduncle of the 

 antennae is shorter than the following joint, and has sometimes a 

 small blunt prominence on its inner margin ; the third joint is 

 short; the flagellum somewhat elongated, with the joints almost 

 naked. The ischium of the outer maxillipedes has a spine at it.3 

 outer distal angle ; the next joint has a prominent lobe on its 

 inner margin ; the three following joints are robust. The chelipedes 

 are robust, but not so broadly dilated as in most species of this 

 genus ; the merus or arm is very short : wrist with broad low pro- 

 minences disposed in longitudinal series on its upper surface, and 



* Vide U.S. Explor. Exped. xiii., Crust, i. p. 411, pi. xxvi. fig. 1 (1852). 



