196 STALK-EYED CRUSTACEA. 
Two of the “Challenger” Peneids assigned to the genus Aristeus by Bate, 
viz. A. armatus and A. rostridentatus, and the two species * doubtfully referred 
to the same genus by Smith differ from the true species of Avisteus 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 pleurobranchiz on each somite from the eighth to the four- 
teenth, the branchial formula in these species being as follows: — 
Somites Wie Allo js x dh SG, Sabi Sane 
Plenrobranchize 0 il Hl aL il a 1 i= of 
Arthrobranchiz 1 1 2 2 2 2 2 O0=— 12 
Podobranchiz 0 1 if! 1 1 il 0 O= 6 
Epipods 1 i i il 1 1 1 0 = (7) 
24+ (7) 
The peculiarities here exhibited appear to be of generic import, and 
these species should be placed together in a genus distinct from Aristeus, to 
which Bate’s provisional name Plestopeneus | may be applied. Peneus edward- 
sianus Johnson,+ assigned to the genus Avisteus by Miers,§ has the terminal 
segment of the mandibular palpus bilobed as in the species of Plesiopeneus, 
and very probably belongs to the latter genus. 
Two of the species (A. semidentatus and A. tomentosus) included in the 
genus Aristeus [_Plesiopeneus| by Bate in 1881, were transferred to Hemipeneus 
in the final “ Challenger” Report of 1888. I suspect that these two species, 
together with Hemipeneus virilis Bate, which is probably the male of ZZ. tomen- 
the gills must not be taken too strictly. He assigns anterior arthrobranchie to the appendages and posterior 
arthrobranchie to the body wall. His description and figure of the gills of A. aztennatus are misinterpreted 
by Professor Smith (Ann. Rep. U. S. Fish. Comm. for 1882, 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 4. occidentalis, is as follows (the Roman numerals are the index num- 
bers of the gills in Duvernoy’s figure) : — 
I. Podobranchia of 8th somite. IX. Posterior arthrobranchia of 12th somite. 
If. Anterior arthrobranchia of 9th somite. X. Anterior Uy G Usin 
III. Podobranchia of 9th somite. XI. Posterior sf ETH rye 
IV. Anterior arthrobranchia of 10th somite. XII. Pleurobranchia of 14th somite. 
V. Podobranchia of 10th somite. XIII. Arthrobranchia of 8th somite. 
VI. Anterior arthrobranchia of 11th somite. XIV. Posterior arthrobranchia of 9th somite. 
VII. Podobranchia of 11th somite. XV. Ke “ of 10th “ 
VIII. Anterior arthrobranchia of 12th somite. XVI. ss se of llth “ 
* Aristeus ? tridens Smith, Ann. Rep. U. S. Fish Comm. for 1882, p. 104, Plate IX. Fig. 1-6, 1884; 
and Aristeus ? foliaceus Smith (= Peneus foliaceus Risso?), Proc. U. S. Nat. Mus., VIII. 188, 1885. The 
former species is identical with 4. armatus Bate. 
t Ann. Mag. Nat. Hist., 5th Ser., VIII. 188, 1881. The type of Plesiopeneus is Aristeus armatus Bate. 
t Proc. Zodlog. Soc. London, 1867, p. 897. 
§ Proc. Zodlog. Soe. London, 1878, p. 308, Plate XVII. Fig. 3. 
