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THE VOYAGE OF H.M.S. CHALLENGER. 



thorax, is considerably shorter than the posterior region, the proportion being about 

 7^:11; the anterior part of the body is also rather broader. 



The head is rather shorter, and narrower than the first segment of the thorax; its 

 dorsal surface is convex and comparatively smooth ; the lateral margins of the head arc 



Fig. l.—Ischnosoma thomstmi, n. sp. 



deeply notched for the insertion of the basal joint of the antennules. The anterior 

 margin is rounded and convex in the middle line. Eyes are completely absent as in ;ill 

 other species of this genus. 



The three first segments of the thorax are approximately equal in size, the second 

 being a trifle shorter than either of the other two. The dorsal surface of these segments 



