196 STALK-EYED CRUSTACEA. 



Two of the ''Challenger" Peneids assigned to the genus Aristwiis by Bate, 

 viz. A. armatus and A. rostridentaius, and the two species * doubtfully referred 

 to the .-^aine genus by Smith differ from the true species of AristcBus in some 

 important respects : the penultimate pair of thoracic appendages are fur- 

 nished with epipods, the antepenultimate pair bear a podobranchia, and there 

 are functional pleurobranchiaj on each somite from the eighth to the four- 

 teenth, the branchial formula in these species being as follows: — 



24 + (7) 



The peculiarities here exhibited appear to be of generic import, and 

 these species should be placed together in a genus distinct from Arisicens, to 

 which Bate's provisional name Plesiopcneus t may be applied. Pcneus edward- 

 sianus Johnson,:]: assigned to the genus Aristmus by Miers,§ has the terminal 

 segment of the mandibular palpus bilobed as in the species of Plcsiopeneus, 

 and very probably belongs to the latter genus. 



Two of the species [A. semidentatus and A. tomentosm) included in the 

 genus Aristceiis \_Plesiopcnevs'] by Bate in 1881, were transferred to Jlcjiiipencus 

 in the final " Challenger" Eeport of 1888. I suspect that these two species, 

 together with Ilcmipenens virilis Bate, which is probably the male of H. tomeru- 



the gills must not be taken too strictly. He assigns anterior arthrobrancbiae to the appendages and posterior 

 arthrobranchiee to the body wall. His description and figure of the gills of A. antennatus are niisinterprelcd 

 by Professor Smith (Ann. Ren U. S. Fish. Comm. for 188'2, p. 409), whose hypothetical formula involves 

 twenty-one gills, while Duvernoy states the number to be sixteen. My interpretation of Duvernoy's figure, 

 by aid of the light thrown upon it by A. occidentalix, is as follows (the lloman numerals are the index num- 

 bers of the gills in Duvernoy's figure) : — 



I. I'odobranehia of 8th somite. IX. Pcsterior .artlirobranchia of 12th somite. 



II. Anterior arthrobranchi.i of 9th somite. X. Anterior " " 13th " 



III. I'oilobraucliia of 9th somite. XI. Posterior " " 13th " 



IV. Anterior arthrobranchia of 10th somite. XII. Plenrobranchia of 14th somite. 

 V. Podobranchia of 10th somite. XIII. Arthrobrancliia of 8tb somite. 



VI. Anterior arthrobranchia of nth somite. XIV. Posterior artlirobrancliia of 9th .somite. 



VIL Podobranchia of 1 Ith somite. XV. " " of 10th " 



Vm. Anterior arthrobranchia of 12th somite. XVI. " " of 11th " 



• ArUlaut? Iridenf Smith, Ann. Rep. U. S. Fish Comm. for 1SS2, p. 104, Plate IX. Fig. 1-6, 1884; 

 and ArUtwus ? foliams Smith (= Pemm foliaceus Risso?), Proc. U. S Nat. iMus., VIll. 188, 1S85. The 

 former species is identical with A. armatus Bate. 



t Ann. Mag. Nat. Hist., .5lh Ser., VIII. 188, 1881. The type of Plesiopcneus is Aristteus armatus Bate. 



X Proc. Zoolog. Soc. London, 18fi7, p. 897. 



§ Proc. Zoolog. Soc. London, 1878, p. 308, Plate XVII. Fig. 3. 



