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5a. Maxilla bearing more than 10 external 
marginal teeth 
pleurobrancheae Della Valle 1880 
5b. Maxilla bearing at most 6 external mar- 
ginal teeth 6 
6a. Ratio of length to width of caudal ra- 
mus about 2.6 lighti, new species 
6b. Ratio of length to width of caudal ra- 
mus about 4 7 
7a. Interior margin of fifth leg bearing distal 
group of slender spinules at distal 
third and a group of slender spinules 
in the middle of the segment 
arenicolus (Brady 1878) 
7b. Interior margin of fifth leg bearing, with 
exception of distal group of slender 
spinules at distal third, no spinules 
or setae 8 
8a. Ventral surface of last segment of uro- 
some with 2 prominent rows of strong 
spinules. solecurti Della Valle 1880 
8b. Ventral surface of last segment of uro- 
some with 2 rows of hardly discerni- 
ble spinules 
teissieri Bocquet and Stock 1958 
9a. Ratio of length to width of caudal ra- 
mus about 1.5 
investi gat oris Sewell 1949 
9b. Ratio of length to width of caudal ra- 
mus much more than 1.5 10 
10a. Ratio of length to width of caudal ra- 
mus about 3 nortoni, new species 
10b. Ratio of length to width of caudal ra- 
mus more than 3.5 11 
11a. Terminal segment of antenna at least 
twice as long as wide 
leptostylis (Sars 1916) 
lib. Terminal segment of antenna about 1.5 
times as long as wide 
dilatatus (Sars 1918) 
12a. Terminal segment of fourth exopodite 
with 4 spines 13 
12b. Terminal segment of fourth exopodite 
with 3 spines 16 
13a. Maxilla with low apical sclerotized por- 
tion, not inclining anteriorly in 
marked angle to remainder of append- 
age hawaiiensis (Wilson 1923) 
13b. Maxilla with apical portion erect, large, 
sharply angled 14 
14a. Exterior margin of fifth leg without 
spinules or setae 
groenlandicus (Hansen 1921) 
14b. Exterior margin of fifth leg with row of 
spinules or setae 15 
15a. Exterior margin of fifth leg bearing only 
about 5 short, stout, conical spinules 
minor Stock 1959 
15b. Exterior margin of fifth leg bearing 
many long, slender spinules or setules 
concinnus (A. Scott 1909) 
16a. Second and fourth segments of anten- 
mile extremely elongate, over 4 times 
as long as wide 
navanacis (Wilson 1935) 
16b. Second and fourth segments of anten- 
nule of moderate proportions, less than 
3 times as long as wide 
pinnae Humes 1959 
The literature contains references to species 
of Anthessius which have not yet received for- 
mal systematic characterization: Pseudomolgus 
sp. Wilson (1921: 15); Pseudomolgus sp. Wil- 
son (1923: 4); and Anthessius sp. Humes and 
Cressey (1958: 935). 
Anthessius Della Valle 1880 
Boeckia Brady 1872^; Brady 1872 A 
Lichomolgus Brady 1880 (pars); auctorum. 
Anthessius Della Valle 1880; Canu 1891; 
Monod and Dollfus 1932; auctorum. 
Hermanella Thompson and Scott 1903 
(pars); auctorum. 
Pseudomolgus Sars 1916; auctorum. 
The complete synonymy of the genus is not 
given here, although the basis for tracing all 
references is provided in the above and the 
bibliographies provided in the references cited. 
There are several systematic problems connected 
with the genus still to be clarified. 
In many regards the diagnosis of the genus 
provided by Della Valle still holds, although 
some of his characters were erroneous. However 
the modern definition may well be based on 
the original description. The body is mostly 
cyclopoid, but some considerable elaboration of 
body processes may occur. The segment of the 
first legs is functionally involved with the ceph- 
alosome in part and may be entirely anatomically 
