Differentiation of Blenniids — STRASBURG 
Northern Marshalls (Bikini, Eniwetok, 
Kwajalein, Rongelap) 
Southern Marshalls (Arno) 
*Line Islands (Fanning) 
Gilberts (Onotoa) 
* Solomons (Bougainville, New Georgia, 
Nissan Group) 
*East Indies (Java, Ste. Barbel) 
Samoa (Apia, Tutuila) 
Tuamotus (Fakarava, Makatea, Makemo, 
Rangiroa) 
Fiji 
Societies (Tahiti, Hereheretue) 
Gambiers (Mangareva) 
Inasmuch as the above band of islands 
crosses the Equator it is obvious that as a 
general rule sea temperatures will be greatest 
near its center and least as the northern and 
southern extremes are approached. Factors 
acting to offset this theoretical distribution 
are ocean currents and the seasons, each of 
which is somewhat variable in itself. These 
two factors, together with limited data on 
hydrographical conditions, make computa- 
tion of accurate temperature values quite dif- 
ficult. In this work surface water temperatures 
have been taken from Sverdrup, et al. (1946: 
charts 2 and 3), and approximations of means 
computed by averaging the values given for 
February and August. These means are listed 
in Table 1, together with other data. 
FAUNAL CONSIDERATIONS 
Istiblennius edentulus was described by Bloch 
(in Bloch and Schneider, Systema ichthyolo- 
giae, p. 172, 1801) from Huaheine Island in 
the Societies. Chapman (in de Beaufort and 
Chapman, 1951: 331) records its distribution 
from various localities throughout the Pacific 
and Indian Oceans and the Red Sea. He also 
mentions (loc. cit.) that the forms of the spe- 
cies occurring in southern Japan, Hawaii, and 
the Marquesas are probably subspecifically 
distinct from the one occupying the rest of 
the distribution. The Japanese and Hawaiian 
forms have been described as full species, 
Istiblennius enosimae (Jordan and Snyder, U. 
299 
S. Nat. Mus., Proc. 25 (1293): 460, 1902), 
and Istiblennius zebra (Vaillant and Sauvage, 
Rev. Mag. Zool., 3 (3): 281, 1875), while the 
Marquesan form is as yet undescribed. Mar- 
quesan specimens were not available for this 
study, and Japanese material was not used 
because of the difficulty of obtaining precise 
water temperatures from along the coasts of 
Japan. 
Principal differences between edentulus and 
zebra are the number of fin rays, the develop- 
ment of the fleshy crest on the heads of 
females, the presence of a tiny cirrus on each 
side of the nape, and the extent to which 
females are covered with small dark spots. 
Chapman (loc. cit.) admits the inconsistency 
of the color pattern as a means of separating 
Indian Ocean edentulus from those of the East 
Indies, and in the writer’s opinion this char- 
acter also is not valid in the Central Pacific. 
The presence or absence of nuchal cirri has 
been studied, and appears to be an excellent 
criterion for distinguishing the Hawaiian rep- 
resentative from the other forms of edentulus. 
Cirri are never present in zebra (based on 244 
specimens), but are always present in the true 
edentulus except for an occasional (injured?) 
specimen lacking the cirrus on one side. Such 
a loss occurs randomly throughout the dis- 
tribution of the species, and is not restricted 
to specimens from areas near the Hawaiian 
Islands as might be expected. 
The relative size of the cephalic crest in 
females is possibly a character worthy of fur- 
ther consideration. This crest is most prom- 
inent in zebra, and examination of large 
numbers of this blenny revealed that crest 
area is related to fish size but also varies 
somewhat at random. Insufficient material 
was available to determine the precise rela- 
tionship of crest area to water temperature. 
MERISTIC DATA 
Table 1 summarizes fin ray counts made on 
edentulus and its close relative, zebra , for 
various portions of their ranges. It also in- 
cludes mean counts for soft rays and data on 
