Description of a Species of Caligus. 229 
Viewed as a whole, the cephalo-thoracic segment is slightly con- 
vex, and has an obtuse ovate form, a little broader posteriorly, 
with an emargination in front, (A, fig. 7,) and a deep sinus on 
each side in the posterior margin, (B.) It is bounded, both ante- 
riorly and laterally, by a thin transparent margin, which appears 
transversely striated, when highly magnified. The lateral mar- 
gin is about four times as wide as the anterior. A row of ex- 
tremely minute curved spines project above the junction of the 
membranous margin, as is exhibited in figs. 1 and. 19. Similar 
spines are scattered over the back; but a very high magnifying 
power and the most favorable light are required to discover them. 
The articulation of the first with the second cephalic segment, 
though mostly imperfect, approaches a perfect joint towards each 
side, (C, fig. 7,) where there is an osseous process in the two seg- 
ments, with opposite articulating surfaces. The process on the 
t segment is narrow, and transversely oblong. That on the 
second is long and slender, and extends to a point laterally in ad- 
vance of the eyes; it is much enlarged at the articulation, and at 
that place resembles the process on the anterior segment. 
The articulation of the cephalic with the thoracic portion of 
the cephalo-thoracic segment of the body is curved parallel with 
the anterior margin of the animal, and terminates on each side, 
hear the centre of each lateral half of the cephalo-thoracic seg- 
ment, (D, fig. 7.) From this point the articulation of the epime- 
ral with the central segments commences. A thin semi-corneous 
margin extends from the cephalic segment, and covers its articu- 
lation with the adjacent parts. The junction of the epimeral and 
cephalic segments is directed towards the anterior portion of the 
lateral margin, but becomes obliterated before reaching it; the 
junction with the thoracic segment is continuous in a curve, con- 
cave inward, to the posterior margin just outside of the sinuses 
in the latter segment. An osseous articulation, similar to that be- 
tween the two cephalic segments, unites the epimeral and ce- 
phalic segments, (E, fig. 7;) the process on the former is long 
and slender, and curves backward, giving firmness to that portion 
of the shell. 
. The thoracie portion of the cephalo-thoracic segment approxi- 
mates to a circular form. The sinuses before referred to, (B, fig. 
7,) are situated in its outer posterior margin. Between each sinus 
the articulation of the epimeral segment, there is a narrow 
