POLYCHELES NANUS. 121 



Polycheles nanus (Smith). 



PMe XXXIIL, Fig. 1, r, IK 



Pentacheles nanus Smith, Ann. Rep. U. S. Fish Comm. for 1882, p. 359, 18S4 ; id. for 1885, p. 651, 

 Plate VII. Kg. l.p, 1886. 



2 fern. 

 1 fern. 



3 males, 3 fem. (1 ovig.). 

 1 fem. 

 6 fem. (1 ovig.). 



These specimens differ slightly, but constantly, from the type specimens 

 from the Atlantic. The edges of the sulcated carina on the sixth abdomi- 

 nal somite are less prominently denticulated and the tubercle at the posterior 

 end of this carina is lower. Further, the spine near the base of the dorsal 

 surface of the telson of the type specimens is reduced to a blunt tubercle in 

 the Pacific examples. In these regards, the Pacific form resembles P. sculp- 

 itis, adding weight to Professor Smith's suggestion that P. nanus may be only 

 a dwarf deep-water variety of P. sculptus. 



An adult ovigerous female measures 58 mm. in length ; carapace 24.5 

 mm. by 16.5 mm. 



The posterior thoracic appendages are chelate in both sexes. 



The branchial formula is as follows : — 



_ (SO 



16+(5r) 



The epipods of the tenth to the thirteenth appendages are represented 

 merely by a plate-like expansion of the base of the stem of the podo- 

 branchia. The epipod of the third maxilliped is very minute and bears 

 no true gill. The podobranchia and the two arthrobranchiae of the tenth 

 somite (cheliped) are much reduced in size. 



