Report on the Crustacea Schizopoda of Ireland. 235 
Mysidopsis hibernica, Norman. 
IPL, SAVibbg inieRs, 4b Gh, 
Survey.—Station 115, off the Skelligs, 62 to 52 fathoms, mud and sand. 
August 20th, 1890. 
_ Previous Record.—Valentia (A. M. N.*). 
The species has hitherto been known from a pair of examples captured by 
Norman in Dr. Jeffrey’s yacht ‘‘ Osprey,” at Valentia in 1870. No note was 
made of the ‘‘circumstances as to the depth, ete.,” under which they were obtained, 
so that our record furnishes the first exact information on this point. The length 
is given by Norman as 15mm. Our solitary example is considerably smaller; 
and, if only young examples were present at the time we were fishing, many may 
have escaped through the meshes of the mosquito-net bag. As usual, the anterior 
appendages are rather defective, the antennal scales having disappeared, and the 
antennules being more or less denuded of setae. Hence the characters of these 
appendages are not available for specific diagnosis. The telson and the inner 
uropod (figs. 4, 5) are, as we think, in sufficiently close agreement with Norman’s 
diagnosis (Ann. Mag. Nat. Hist., s. 6, October, 1892, p. 165, pl. ix., figs. 2, 3, 4) 
to warrant us in referring the specimen to W, hibernica. It will be noticed, how- 
ever, that the apex of the telson diverges slightly from the type. In Norman’s 
figure there is shown but a slight emargination of the posterior border between 
the inner pair of terminal spines, whereas Mr. Green’s drawing shows that the 
Skelligs specimen hag a distinct notch in this position; while the terminal spines 
(the longer of which have lost their points) are by no means symmetrical. Slight 
variations and abnormalities of this structure must be quite familiar to every 
student of the family. If Norman’s figures 2 and 3 (/oc. cit.) are drawn to the 
same scale, the telson must, relatively to the length of the inner uropod, be rather 
shorter in the Skelligs example than in the type. We believe that we have 
evidence, from the analogy of other members of the family, that such a difference 
is often explicable by the size of the specimens, the length of the telson tending 
to increase with age. In our specimen the lateral margins of the telson have 
fewer spines than are shown in Norman’s figure, as, indeed, might be anticipated 
from its small size (cf. especially Schistomysis spiritus). 
The typical structure of the telson cannot be held to be certainly known until 
more specimens have been examined. Although the asymmetry of the Skelligs 
example suggests abnormality, it is quite possible that a notch in the posterior 
border is more usual than a simple emargination. 
