REPORT ON THE CRUSTACEA MACRURA. 273 



Dana says, " Penult, abdominal segment as long as two preceding, and having a few 

 minute spines on the back of it." 



There are no small spines on the dorsal surface of the sixth somite of the pleon in our 

 specimen ; but they might have been rubbed off. Undoubtedly Dana's specimen, although 

 twice the size of those in the Challenger collection, is immature. 



There is no evidence of sexual character such as is visible externally in mature forms ; 

 all the pleopoda are single-branched, a circumstance that is not comformable with the 

 condition of a mature specimen of the genus Penseus, but is consistent with that of 

 Sicyonia. In Haliporus the two branches are present but in a very unequal condition. 



It must therefore be left for future research to determine the relation of Penseus 

 gracilis to the adult stage. 



Penseopsis, A. Milne-Edwards. 



Penxopsis, A. Milne-Edwards, MS. 



Sp. B., Ann. and Mag. Nat. Hist. ser. 5, vol. viii. p. 182, 1881. 



Like Penseus, but with the nagella of the first pair of antennas longer than the 

 carapace. 



There is no species of this genus in the Challenger collection. 



This genus is very closely allied to Milne-Edwards' second division of Penseus, or 

 those Peneids in which the nagella of the first pair of antennas are longer than the 

 carapace. 



Penseus tenellus approaches nearer to it than any other in the Challenger collection, 

 but the nagella are not longer, if even quite as long, as their peduncle, although together 

 they are longer than the carapace. 



Philonicus, 1 n. gen. 



Carapace armed with four teeth on each side, namely, the first antennal tooth on the 

 frontal margin, one behind it, one behind the second antenna, and one on the hepatic 

 region, and produced anteriorly to a sharp-pointed rostrum that is laterally compressed 

 and armed on the upper surface with small teeth. 



The ophthalmopoda are Particulate, shorter than the' rostrum, and support an 

 ophthalmus of moderate proportions. 



The first pair of antennas has a prosartema and stylocerite attached to the first 

 joint, and terminating in two extremely long and subequally sized flagella, the upper of 

 which is very slender, the lower very broad, but not grooved on the upper surface to 



1 Qthovtlxos, a rival. 

 (ZOOL. CHALL. EXP. — PART LII. 1886.) *ff 35 



