SEA-BREAMS. 
57 
Obs. In order to comprehend the mutual relations of the spe- 
cies within this group of the genus Spams , it must be of interest 
to see how far certain relations point to a fixed direction of deve- 
lopment in the difference of species. In several respects, it is true, 
this difference is connected with the difference in the depth of the 
water where they live, and this consists, as usual, in the greater or 
smaller size of the eyes. To a great extent, too, it may depend, as 
we see in some of the corresponding circumstances in the Salmonidce a , 
on the preponderating influence of sex on the development, on which 
point, however, we cannot give any opinion here owing to the lack 
of the necessary information. In other cases, on the contrary, the 
difference in form runs parallel to the individual development, and 
enables us to trace the natural, generic course of development. The 
appended comparative table gives examples of the relations mentioned, 
and simultaneously states the most apparent and constant characters 
of three species represented by one specimen of Spams mormyrus 
(Linnaeus's type-specimen of Sp. hurta ), one specimen of Sp. erythri- 
nus from Nice, kindly lent to me by the Museum of Upsala Uni- 
versity, and two specimens of Sp. centrodontus , the younger from 
Bohuslan and the older from the Atlantic outside Bergen. 
Length of the body, expressed in min... . . 
Breadth of the snout 6 in % of the length of the lower jaw 
„ „ „ „ ,. „ „ „ interorbital space 0 _ 
Interorbital space ,, „ „ ,, length of the head 
Length of the snout d ,, „ „ „ „ „ „ „ 
Base of the anal fin in % of the distance between the tip of the snout and the beginning of the dorsal fin 
Horizontal diameter of the eye in % of the length of the body... 
., ,, ,, „ ,, „ „ ,, ,, ,, „ ., snout 
„ „ „ „ „ „ ,, ,, ,, breadth ,, „ interorbital space 
„ ,, „ ,, „ ,, ,, „ „ length „ ,, lower jaw.. 
„ ,, „ „ ,, „ „ ,, „ least depth of the tail 
Length of the snout in % of the length of the body 
Base of the anal fin „ „ „ „ „ „ „ head 
Postabdominal length 0 ,, „ „ ,, distance of the dorsal fin from the tip of the snout 
Breadth of the snout in % of the base of the anal fin 
Postabdominal length in % of the length of the body 
Base of the anal fin „ „ „ ,, ,, „ „ „ 
Least depth of the tail „ ,, ,, ,, „ ,, ,, „ 
Length of the pectoral fins „ „ ,, „ „ „ ,, „ 
„ „ „ ventral fins in % of the length of the pectoral fins.. 
Spams 
mormyrus 
Spar us 
erytlirinus 
Spams 
centrodontus 
248 
224 
292 
333 
53.6 
51.9 
50 
48.7 
71.4 
66.6 
61.5 
56.2 
28.4 
31 
31.7 
33 
51.3 
43.4 
30.5 
30 
41.4 
48.3 
53.3 
54.7 
5.7 
7.4 
8.2 
8 
19 
24.3 
29.2 
27.3 
37 
56 
96 
91.4 
66.6 
78.6 
92.3 
82.8 
50 
61.i 
75 
71.6 
60.9 
94.3 
100 
96.4 
15.3 
13.i 
8.6 
8.7 
55.4 
57.3 
68.3 
66 
64.6 
69.5 
78.i 
77.8 
36. g 
36 
28.6 
28.1 
25.8 
25.4 
28.i 
27.3 
16.5 
17.4 
19.i 
19.2 
9.2 
7.8 
8.2 
8.2 
23.o 
33 
29.4 
30 
70. o 
51.7 
57 
54 
The differences arising from the direction of development com- 
mon to the whole genus, expressed in their proportions, run uni- 
formly through all these four columns, rising or falling. The other differ- 
ences are those with regard to which we have to look for the grounds 
for the interruption of the serial arrangement in local or sexual circum- 
stances. The comparison shows that Spams mormyrus , which lives 
in the shallower parts of the Mediterranean, seems in its characters 
to come nearest the original type of the genus, which might have 
been especially distinguished by smaller eyes, shorter pectoral fins 
and a higher cheek, as well as a higher peduncle of the caudal fin. 
This species is also distinguished by the transverse bands, which call 
to mind the juvenile colouring of other species. 
a Smitt: Kritisk Forteckning ofv.er de i Rilcsmuseum befintliga Salmonider, K. Vet.-Akad:s Handl., Bd. 21, N:r 8. 
b The breadth of the snout here, as everywhere in this work where nothing else is remarked, is measured across the outer edges of 
the knobs of articulation of the maxillaries. 
c The breadth of the interorbital space here represents the breadth of the forehead from one orbital margin to the other, across the 
middle of the eyes , and is thus far from always the least breadth of the forehead. 
d The length of the snout is measured from the anterior margin of the orbit to the middle of the tip of the snout. Steindachnf.k 
(1. c.) has evidently taken this measurement in another way. 
e As in the treatise on the Salmonidee of the Royal Museum mentioned above, I give this name to the distance between the foremost 
point of the insertion of the ventral fins and the beginning of the anal. 
Scandinavian Fishes. 
8 
