Gill Arches of Teleostean Fishes — Nelson 
397 
between the species examined may be depicted 
by the rather linear reduction in gill arch ele- 
ments (Table 1), with Echelus being the most 
primitive form and Leptenchelys the most 
advanced. In view of the variability exhibited 
in gill arch structure, a supplementary study 
was made on the sensory canal pores of the 
following material, mainly from the University 
of Hawaii collections: 
Ahlia egmontis, 2 specimens, 103, 235 mm, 
Puerto Rico; Myrophis punctatus, 3, 127-139 
mm, Texas Coast; M. uropterus, 1, 82 mm, 
Palmyra; Muraenichthys cookei , 1 Oahu, 4 
Johnston, 128-225 mm; M. macropterus, 1 
Hull, 3 Makatea, 102-200 mm; M. gymnotus, 
1 Aitutaki, 1 Eniwetok, 1 Johnston, 1 Raro- 
tonga, 4 Tahiti, 84-136 mm; M. laticaudata, 
1 Aitutaki, 1 Bikini, 1 Eniwetok, 2 Onotoa, 1 
Rongelap, 2 Tonga, 92-139 mm; M. schultzei, 
1 Arno, 1 Guadalcanal, 3 Johnston, 1 Papeete, 
53-120 mm; Leptenchelys labialis, 1 Eniwetok, 
5 Johnston, 122-136 mm; Schultzidia john- 
stonensis, 2 Johnston, 1 Midway, 2 Oahu, 84— 
163 mm. 
The number and pattern of sensory pores 
of the head exhibited great stability in speci- 
mens of the some species, sometimes being dis- 
tinctive enough to permit identification on this 
basis alone. 
The pattern of cephalic pores basic to the 
group is probably that shown in Myrophis 
punctatus, M. uropterus, Ahlia egmontis, 
Muraenichthys cookei, M. laticaudata, M. mac- 
ropterus (Fig. 21), and Pseudomyrophis nimius 
(Bohlke, 1960:2-4, fig. 1). The pattern in 
Echelus apparently is secondarily simplified 
(Allis, 1903; Gosline, 1952), as seems to be 
that also of Hesperomyrus (Myers and Storey, 
1939). 
The pores of the head are easily divided into 
groups (paired unless otherwise indicated) : a 
supraorbital group of five pores, beginning 
with the one on the underside of the snout; 
a median interorbital pore; a postorbital pore; 
three pores below the eye; two between the 
nostrils; five in a row along the lower jaw; 
three over the preopercle, forming an angle of 
about 90 degrees; a series of five across the 
nape, including the anteriormost pore of the 
lateral line on either side. 
The supraorbital pores, including probably 
those on the underside of the snout (Allis, 
Figs. 21-25. 21, Muraenichthys cookei, sensory 
pores of the head and anterior trunk. 22, M. gymno- 
tus . 25, M. schultzei. 24, Schultzidia johnstonensis. 
25, Leptenchelys labialis. 
