16B Canadian Arctic Expedition, 1913-18 
SPIONIDAE. 
Spio mimus, n. sp. 
The one specimen of this form secured is about 15 mm. long. It is broadest 
anteriorly near the ninth somite, in front of which it is pointed and caudad 
of which it narrows continuously to the posterior end at first gradually and then 
more strongly. The specimen is complete and consists of forty-five segments 
or near that number. ; 
Type specimen.—Cat. No. 35, Victoria Memorial Museum, Ottawa. 
The prostomium protrudes anteriorly in a rounded process much as in 
S. filicornis. The sides are subparallel back to the level of the first parapodia 
from where they converge caudad, the caudal end of the prostomium being 
narrowly rounded and lying at the anterior edge of the second setigerous somite. 
The median ridge of the prostomium rises posteriorly and expands into a rounded 
elevation on which the eyes are borne. There are two pairs of eyes with slight: 
pigmentation on one side indicating a possible intermediate eye. The posterior 
eyes are smaller and much nearer to each other than the anteriors. (See Pl. ITI, 
fig. 1). 
F — all of the usual well-developed biramous type. Both notopodium 
and neuropodium throughout have well-developed postsetal lamelle which in 
general are low, vertically elongate and evenly rounded. The neuropodial 
lamella at the posterior end becomes relatively longer, more cirriform. The 
dorsal lamella is fused at the base with the branchia. It remains at the same 
general form over most of the body but at the posterior end becomes gradually 
increased in length and finally much elongate and branchiform. The branchiz 
are present on all parapodia excepting the last two pairs. The first branchie 
are short, the following ones increasing in length and soon attaining the maximum 
when they ordinarily extend more or less obviously beyond the middorsal 
line and are proportionately heavy. At the posterior end the branchiw become 
reduced and in the last few pairs are much exceeded in length and thickness 
by the dorsal lamella which in the meantime has become cirriform and some- 
times a little clavate. The last branchiz occur on the third pair of parapodia 
from the last and are merely slight tubercles. (See Pl. III, fig. 3). 
Only capillary sete are present in the first sixteen or seventeen pairs of 
parapodia. Those of the posterior series are broad, bilimbate sete with fine, 
often curving tips. The anterior sete are finer. The superior dorsals are of 
the finer capillary type. On the seventeenth parapodia crochets make their 
appearance in the neuropodial fascicle, at first one and two in number, and then 
increasing to nine, which seems to be the prevailing number. The crochets 
are of nearly uniform width over most of their length, the free portion moderately 
evenly curving. At the distal end of the shaft narrows to a rather slender 
neck above which it terminates in two teeth of which the apical is much smaller 
and acute. Distal end completely sheathed, the sheath widening distad and 
then rounded at the end. Shaft strongly fibrillate. (See Pl. III, fig. 4). 
The caudal end of the body ends in four papille of which the ventral are 
much stouter than the dorsals, reversing the condition, e.g., in S. mesnili (Euspio 
McIntosh). (See Pl. III, fig. 2). 
Locauiry.—Alaska: Collinson point. Station 270. September 20, 1913. 
“ Pelagic under 5 inches of ice over 1 foot of water. Lagoon at Collinson point.” 
One specimen. 
This species resembles S. filicornis (O. F. Miller). It differs in the character 
of parapodia and branchie in the posterior region, the great reduction of the 
branchie and the elongate, cirriform or subcirriform character of the lamella, 
etc. Contrasting conspicuously with the condition in filicornis, in which the 
branchiz remain long and the lamelle are not thus modified. The crochets 
first appear farther caudad than in filzcornis, etc. 
