136 = M. W. Lilljeborg on two remarkable Crustacea. 
With regard to its structure, Bythotrephes has the greatest 
affinity to the genera Polyphemus, Podon, and Evadne, and 
evidently belongs to the same group. From the first two, 
which it most nearly resembles, it differs in its more perfect 
abdomen and long caudal bristle. From Evadne it deviates even 
more widely. 
It appears to be very rare. Baron Cederstrém took a few 
specimens in the lakes m Jemtland and in Wombs Lake, in 
Scania, which were communicated to me; and I have myself 
taken a solitary specimen in the Malar Lake, near Flottsund. 
Of this I noticed that it remained at the bottom of the vessel 
in which it was contained, in consequence of the long caudal 
bristle being a hindrance to it in swimming. It is therefore 
probable that, in its free state, it abides less in proximity to the 
surface of the water than the Polyphemus, and that it is from 
this cause that it is so seldom obtained. F. Leydig found it in 
the stomach of Coregonus Wartmanni, taken in the Lake of 
Constance, in Switzerland. He did not succeed in procuring 
one alive, whence he supposes that it dwells near the bottom. 
EXPLANATION OF PLATE VIII. 
Fig. 1. Leptodora hyalina; a full-grown female, seen from above and 
somewhat from the side: 6, the antennz of the second pair ; 
k, matrix. | 
Fig. 2. A younger female, seen from the side: a, an antenna of the first 
pair; 0, base of an antenna of the second pair; f, gullet; g, sto- 
mach; h, heart; 7, ovaria; k, matrix; /, head-ganglia. 
Fig. 3. One antenna of the first pair. 
tg. 4. Both branches of one antenna of the second pair. 
fig. 5. One mandible seen under a glass cover. 
Fig. 6. Upper lip lifted up (d), under lip (e), and both mandibles in their 
natural position. 
Fig. 7. Ovarium. 
Fig. 8. The front of the body, seen from above, to show the muscles pass- 
ing to the second pair of antennz: a, antennz of the first pair ; 
J, gullet; h, heart; m, the nerve-cord, passing from the back 
ganglion of the head, which behind separates and encompasses 
the gullet. 
Fig. 9. Bythotrephes longimanus; a full-grown female: a, antenne of 
the first pair: 5, antenna of the second pair; c, a mandible ; 
d, legs; e, upper lip; &, matrix. 
Fig. 10. A younger specimen, | millim. long; sex unknown: f, heart. 
Fig.11. A leg of the third pair, seen from the inner side: a, with an 
appendage provided with prickles or points. 
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