270 



Prof. S. I. Smith on the 



Of the three genera into which Bate has separated the forms 

 of the " Willemoesia group," our species should be referred to 

 Pentacheles ; but, on account of the at present uncertain tenure 

 of these genera, I have referred it provisionally to Heller's 

 Polycheles. It is apparently very distinct from any of the 

 Atlantic species described by Heller, Willemoes-Suhm, or 

 Bate ; but, judging from the very short descriptions given by 

 the last author, it appears to be closely allied to his Penta- 

 cheles auriculatits, obtained by the ' Challenger ' expedition off 

 the Fijis. Our specimen is a male, 92 millims. long. It is 

 described in detail in the l Proceedings of the National Mu- 

 seum, Washington,' for 1879, as Polycheles sculptus; andl wish 

 here to call attention to a few points in its structure only. 



The anterior margin of the carapax, as seen from above, is 

 concave in outline, so that the lateral angles are much in ad- 

 vance of the rostrum. About a third of the space between the 

 median line and the lateral angle on each side is occupied by 

 a very deep orbital sinus completely 

 filled by a large ophthalmic lobe 

 (fig. 1). Just behind the orbital 

 sinus there is a smooth and evenly 

 curved depression in the surface of 

 the carapax, exposing a small area 

 on the posterior part of the ophthal- 

 mic lobe. 



The ventral region of the carapax 

 on each side is divided longitudinally 

 into three approximately equal parts 

 by two carinas : the outer (marking 

 the pleuro-tergal suture?) extends 

 from the anterior margin at the base 

 of the antenna toward the postero- 

 lateral margin ; the inner extends 



Ffg.L 



J>0& 



along the branchial region from near 



Dorsal view of the ante- 

 rior portion of the right side 

 of the carapax : a, antennal 

 scale ; b, proximal segment 

 of antennula ; c, ophthalmic 

 lobe. 



the base of the first pereiopod to the 

 postero-lateral angle of the carapax. 

 The outer of the three longitudinal 

 regions thus marked out is divided transversely by the 

 cervical suture ; and the anterior portion (subhepatic region) 

 is divided transversely into an anterior and a posterior lobe 

 by a groove nearly or quite as conspicuous as the cer- 

 vical. In the frontal margin of this anterior lobe and near 

 its inner side there is a deep sinus corresponding to the orbital 

 sinus of the dorsal surface, but not quite as wide, and open 

 nearly to the dorsal surface, except where it is crossed by a 

 protuberance from the ophthalmic lobe (fig. 2). 



