SMELTS. 
865 
chiostegal apparatus differs from that of the Salmons in ' 
its fewer rays, 7 or at most 8, the anterior needle- 
shaped, the last three broad and ensiform. The oper- 
cular apparatus is distinguished from that of the Sal- 
mons principally by the fact that the preoperculum is 
attached to the upper part of the hyomandibular bone 
(which is here elongated in the form of a, backward 
process) only at the very top, in common with the ar- 
ticular knob of the operculum. Below the said process 
asq p psq 
C 
Fig. 218. A, Scale from the lateral line of Osmerus eperlanus with 
imperfectly closed duct, magn. 8 diam. For the further elucidation 
of its structure are added a scale ( B ) from the lateral line of a 
Salmo trutta (9 338 mm. long, from Norrkoping), also magnified 
8 diameters, and a section (G) of 2 1 /, scales (magn. 10 diam.) from 
the lateral line of a large Salmon, t , duct of the lateral line; asq, 
anterior part of the scale; psq, posterior part thereof; p, pore in the 
scale (answering to the deep incision in the scale from the lateral 
line of the Smelt), through which the nerve of the lateral line passes 
from one scale to the next, after sending out a ramification with 
a sensory organ into the duct on the outer surface of the posterior 
part of the scale. 
is a large opening between the preoperculum and the 
hyomandibular bone, which in front, on the other hand, 
expands into a disk, forming a stronger support for 
the palatine arch, and is itself strengthened b} T a down- 
ward ridge at the middle of its inner surface. The 
spinal column is similar to that of the Salmons; but 
the haemal arches are not completely closed until they 
reach the beginning of the caudal part. The series of 
bones which in the Salmons forms the postclavicular 
apparatus, is here represented by a small, round and 
thin, disk-shaped bone at the hind inferior extremity 
of the clavicle, with its upper part attached inside the 
lower angle of the posteriorly expanded disk of the 
latter. The pelvic bones are weak and resemble those 
of the Salmons. 
The scales of the Smelts are thin, on the sides of 
the body elliptical, with longitudinal axis set crosswise 
(up and down), on the belly more rounded or of broad 
oval shape. In texture they resemble the scales of the 
Salmons, without radiating grooves, but with more or 
less numerous and dense concentric stria?. The indi- 
stinct nucleus is eccentric and lies in the anterior (in- 
serted) part of the scale. The lateral line is distinct 
only on the anterior part of the sides. Its scales are 
deeply cloven behind, where the canal of the lateral 
line has its course, and the duct belonging to each 
scale, and surrounding the canal, in front of this cleft, 
and on the outside of the scale, is open or at least 
imperfectly closed — as in the earlier developmental 
stages of more complete lateral lines - — the margins of 
the primitive canaliculate duct not coalescing, even 
where one of them overlaps the other (fig. 218, A). 
The scales of the Smelt are further distinguished by 
the absence of the layer of silvery pigment which else- 
where lines the scales where this colour appears. The 
silvery lustre is indeed present in a longitudinal band 
along the sides of the Smelt; but on removing the 
scales we distinctly see that the coat of pigment lies 
in the skin under the scales. 
The relation to the Salmons has already been ex- 
pressed in the above generic characters. But this re- 
lation, as paleontology seems to indicate, is probably 
one of development as well, Osmerus standing nearer 
to the common ancestors of the genera. This appears 
most clearly on a comparison of the average figures 
expressing the corresponding relations of form in the 
two genera. 
From the above table of averages (p. 853) we 
easily see that the position of the dorsal tin, expressed 
in the distance from the tip of the snout to the be- 
ginning of the base of this tin, becomes more forward 
with age — and the averages for the several ages show® 
that this alteration of growth is greatest during the 
earlier and earliest stages. The said distance decreases 
both in proportion to the length of the body and to 
Cf. Smitt, Riksmuseets Salmonider, pp. 11 and 25. 
