336 Merrill—Structure and Affinities of Bunops ScuUfrons. 
nearest to Bunops in habit, the ventral margins of the valves 
approach in front, gape in the middle, and approach again be¬ 
hind, (Plate XIV, Fig. 7). This is true of Macrothrix and of 
most of the family. In Bunops , the infolding of the valves is a 
peculiar structure unlike anything in the other genera. The 
arrangement allows the animal to feed by the aid of its anterior 
appendages, and at the same time protects the hinder limbs, 
which are used for respiration, from the parasitic algse, which 
so often load the legs of Macrothrix. In Acantholeberis an im¬ 
perfect protection is given by the spines of the carapace, and 
these are are so arranged in Streblocerus and Drepanothrix as to 
form a kind of grating over the opening of the valves. The 
mud-haunting Ilyocryptus protects its legs by completely en¬ 
closing them within the valves. 
The structure of the forehead is one of the most interesting 
features of the genus. The flattened or even concave forehead, 
with the fornices continued as its kite-shaped edges, and the 
boss over the eye, are peculiar to the genus. It is interesting to 
see how this structure is related to and derived from the cor¬ 
responding part in the other genera. In Acantholeberis and 
Macrothrix latirostris, the dorsum of the head is rounded and 
projects evenly out to the apex, where the antennules are in¬ 
serted. In Latlionura , Ophryoxus and M. rosea , the even curve 
of the dorsum is altered. The posterior part continues the out¬ 
line of the back, and the anterior part bends abruptly downward, 
so that its downward course is nearly at right angles to the poster¬ 
ior part. At the same time, the fornices are developed into strong 
ridges which extend to the rostrum, and project on each side. 
Thus the head (PI. XIV, Fig. 7), as seen from above or below, 
presents three parts, the first of which is a median ridge 
rounded over from side to side and bent dorso-ventrally, which 
is obviously the dorsum of the head as seen in Acantholeberis. 
On each side of this ridge is a valley rising on each side into 
the sharp ridges of the fornices; behind the median ridge, and 
near the angle of the head, lies the eye. 
In Drepanothrix , the crest, or rather the keel, is carried out 
in an even curve to the apex of the rostrum. The head is ac¬ 
cordingly greatly compressed, the antennules are inserted 
