1344 THE VOYAGE OF H.M.S. CHALLENGER. 



in profile, the prominent teeth in this view twelve in number, pretty widely spaced ; the 

 surface of the mandible for some distance behind the tubercle scabrous with minute teeth 

 or prickles. There is no trace of a palp. 



First Maxillw. — The pair appear to be connected by a thin membrane ; no inner 

 plate was perceived ; the outer plate distally cut into three very sharp teeth ; the inner 

 margin of the palp straight, serrate, carrying at its apex a small sharp spine-tooth, the 

 outer margin convex, smooth, the distal convex, with slight outward directed serrature ; 

 both plate and palp being so bent that the distal margins of one maxilla may antagonize 

 with those of the other. 



Second Maxillae. — These are obscure, probably small and unarmed. 



Maxillrpeds. — The base is formed by an oblong plate having a flat distal margin 

 with its corners rounded and a small spinule projecting near each of them ; a little 

 above the middle of this, and not nearly reaching its distal margin, is placed a small 

 triangular inner plate with rounded apex, and above this are placed the two outer plates, 

 which are smooth-edged, apically narrowed, the outer margin convex, the inner carrying 

 three minute spinules. All these organs are small, thin in texture, and transparent. 



The heart has very thin and delicate walls, apparently with three pairs of venous 

 ostia ; it reaches just into the sixth or penultimate segment of the perseon. 



First Gnailiop>ods. — Side-plates of this and the following segments shallow, but 

 definitely marked, not overlapping; the coalesced first and second segments having separate 

 side-plates for each segment. The first joint in this and the six following pairs of limbs 

 attached at the lower extremity of the side-plate, longer than the three following joints 

 together, and like them apically encircled with one or two rows of minute denticles, the 

 lateral margins smooth ; the second joint not longer than broad ; the third a little longer 

 than the second, not under-riding the fourth; 1 the fourth joint elongate, a little curved, 

 more than half as long as the first, the hinder margin as in the preceding joint a little 

 furred, the fifth joint more than half the length of the fourth, much narrower, a little 

 curved ; the distal part (as is the case with this joint in the other limbs) speckled as if 

 with scale-markings ; the finger exceedingly small, acute. This and the six succeeding 

 pairs of legs are all arranged on the same plan, and all for the reception of gland- 

 cells, in particular the muscles of the long first and fourth joints being relegated to a 

 mere corner of the distal end, leaving so large a space va,cant as to give a rather peculiar 

 appearance to these transparent limbs. 



Second Gnathopods. — Similar to the first but longer. Branchial vesicles quite smooth, 

 oval, a little wider than the first joint and about two-thirds as long. The first three joints 

 of the limb rather stouter and slightly longer than in the first pair ; the fourth joint as 



1 The rule laid down by Spence Bate, Brit. Mus. Catal. Amph. Crust., p. 89, footnote, that "the meros always 

 overrides the carpos in the pereiopoda and underrides it in the gnathopoda," is of very limited application to the 

 gnathopods of the Hyperina, although so constant in the Gammarina. 



