Gillichthys mirabilis — BarloW 
53 
FIG. 2. Head length versus standard length. Gulf of 
California populations: open triangle, San Felipe (El 
Marino); open square, Mulege; open circle, Bahia 
Cholla, 1954; closed triangle, Guaymas (Estero Boco- 
chibampo); closed circle, Agiabampo. Pacific Coast 
populations: closed circle, San Francisco Bay (Alviso 
ponds); open triangle, Goleta; closed square, Newport 
Bay; open circle, San Elijo Lagoon; closed triangle, 
Estero Punta Banda; open square, Bahia San Quintin. 
Salton Sea population: open triangle, 1953; open 
circle, 1954; open square, 1955. 
smallest and largest fish measured, i. e., the lines 
are parallel. Therefore, differences between 
slopes of arithmetic plots presented here are 
of no biological significance. 
Upper Jaw 
The analysis of upper jaw measurements is 
complicated by the curvilinear relationship be- 
tween jaw length and standard length. (Here- 
after, upper jaw is referred to as jaw.) This dif- 
ficulty is alleviated somewhat by fitting two re- 
gressions through the data; one line for fish 
greater than 90 mm, and another for the smaller 
specimens (Fig. 3). The change in slope is an 
artifact of the arithmetic plot; relative growth is 
only slightly curvilinear. The situation is also 
complicated by the sexual dimorphism of jaw 
length in adult fish. The average length of the 
jaw is slightly greater in males, even though the 
range is about the same in both sexes. Conse- 
quently, the results of the covariance tests (Table 
3) should be regarded with skepticism, since 
some of the assumptions underlying the test are 
not entirely satisfied. 
The jaw of fish from the Gulf is about equal 
to, or slightly larger than, the jaw of Pacific 
Coast fish when specimens of the same length 
are compared. On the same basis, the jaw is 
much shorter in fish from the Salton Sea. 
If jaw lengths are compared as a function of 
head length instead of standard length, the jaw 
is still relatively longest in Gulf fish and shortest 
Fig. 3. Upper jaw length versus standard length. 
Gulf of California populations: open triangle, San 
Felipe (El Marino); open square, Mulege; open 
circle, Bahia Cholla, 1954; closed triangle, Guaymas 
(Estero Bocochibampo) ; closed circle, Agiabampo. Pa- 
cific Coast populations: closed circle, San Francisco 
Bay (Alviso ponds); open triangle, Goleta; closed 
square, Newport Bay; open circle, San Elijo Lagoon; 
closed triangle, Estero Punta Banda; open square, Ba- 
hia San Quintin. Salton Sea population: open triangle, 
1953; open circle, 1954; open square, 1955. 
