Thoracic Cirripedia from a Guyot — Z ullo and Newman 
369 
of Annandale (1906*z, p. 148) from the 
Gulf of Manaar (Nilsson-Cantell, 1938:30). 
Balanus ( Solidobalanus ) compressus Hoek 
(1913:202, pi. 19, fig. 17; pi. 20, figs. 1-7); 
Banda Sea, Timor Sea. 
Balanus ( Solidobalanus ) echinoplacis S tub- 
bings (1936:45, figs. 20a-k) ; Zanzibar 
area. 
Balanus ( Solidobalanus ) hawaiensis Pilsbry 
(1916:222, pi. 48, figs. 1-lg; text figs. 
70a-c); Hawaiian Islands. 
Balanus ( Solidobalanus ) maldivensis Borra- 
daile (1903:442, fig. 118); Maidive Islands. 
Balanus ( Solidobalanus ) occidentalis S tub- 
bings (1961:34, text figs. 8-11); tropical 
West Africa. 
Balanus ( Solidobalanus ) pseudauricoma Broch 
(1931:72, figs. 25a-i); Molucca Sea, Japan. 
Balanus ( Solidobalanus ) socialis Hoek (1883: 
150, pi. 13, figs. 23-28); Arafura Sea 
(Hoek, 1883); Moluccas, Flores Sea (Hoek, 
1913); Java Sea (Nilsson-Cantell, 1934*0 ; 
British North Borneo (Nilsson-Cantell, 
1937) ; Gulf of Manaar, Ceylon (Nilsson- 
Cantell, 1938); Japan (Utinomi, 1949). 
Synonyms : Balanus aeneas Lanchester 
(1902:370) and B. aeneas Lanchester of 
Annandale (1906*z:l48) from the Malay 
Peninsula and the Gulf of Manaar, re- 
spectively (Pilsbry, 1916; Nilsson-Cantell, 
1938) . 
Balanus ( Solidobalanus ) solidus Broch (1931: 
76, figs. 26a-i) ; Japan. 
Balanus ( Solidobalanus ) tantillus Pilsbry 
(1916:224, pi. 48, figs. 2-2 e; text figs. 
72a-c); Sulu Archipelago. 
Balanus ( Solidobalanus ) thompsoni Stubbings 
(1936:43, figs. 19a-h); Gulf of Aden. 
Balanus nascanus resembles B . hawaiensis 
Pilsbry from the Hawaiian Islands. However, 
there are certain characters which distinguish 
the new species. The articular ridge of the 
scutum of B. nascanus is erect, whereas Pilsbry 
(1916:222) describes that of B, hawaiensis as 
"somewhat reflexed.” Pilsbry did not describe 
the pit for the lateral depressor muscle, but that 
of the figured scutum (Pilsbry, 1916, pi. 48, fig. 
If) is only vaguely indicated, whereas the lat- 
eral depressor pit of B. nascanus is deep and 
prominent. The exterior of the scutum of the 
new species is ornamented by fine, closely spaced, 
radial striae which are not present in B. hawai- 
ensis. The tergum of B. nascanus is narrower 
than that of B. hawaiensis. In addition Pilsbry 
( 1916:222) describes the tergal spur of B. ha- 
waiensis as "very short, tapering to a rounded 
end.” Measurements of his figures indicate that 
the length of the spur is approximately equal to' 
one-half the width of the spur at the basal 
margin. The spur of B. nascanus is longer (its 
length being nearly equal to the spur width), 
more pointed distally, and placed closer to the 
basiscutal angle. The margin of the labrum of 
B. nascanus differs in being sinuous rather than 
straight, and the mandible differs in having a 
pointed, bifid third tooth on the cutting edge 
and accessory teeth above and below the fourth 
tooth as in B. tantillus (Pilsbry, 1916, text fig. 
72c). 
Balanus nascanus can be distinguished from 
B . ciliatus, B. compressus , and B. socialis by the 
the absence of teeth or hooks on cirri III and IV. 
Balanus astacophilus can be separated by the 
shorter, broader tergal spur, and by the greater 
number of teeth both on the mandibles and on 
the labrum. In B. auricoma the tergal spur is 
more distantly removed from the tergal margin 
and the mandible does not possess the distinc- 
tive trispinose inferior angle of B. nascanus and 
B. hawaiensis. Balanus echinoplacis, B. pseu- 
dauricoma, B. solidus, and B. thompsoni also 
lack the trispinose inferior angle on the man- 
dible, and can further be distinguished by their 
possession of a short, broad, obliquely truncate 
tergal spur. In addition; B. echinoplacis is de- 
scribed as having a porous basis, whereas that 
of B. nascanus is solid. 
Balanus maldivensis and B. tantillus are sim- 
ilar to B. nascanus in the form of the opercular 
valves. Balanus maldivensis, however, can be 
distinguished by the horizontal summits of the 
radii and the form of the mandible, and B. tan- 
tillus differs in having the tergal spur confluent 
with the basiscutal angle. The recently described 
West African species B. occidentalis resembles 
B. nascanus in the characters of the trophi, but 
differs in the possession of teeth on the anterior 
border of the posterior ramus of cirrus III, in 
the lack of radial striae on the exterior of the 
scutum, and in the broader tergal spur placed 
farther from the basiscutal angle. 
