370 REV. A. 51. NORMAN AND MR. G. S. BRADY 



is usually large and acute, and beneath which the anterior an- 

 tennae are wholly or partially concealed. Posterior antennae two- 

 branched, both branches three-jointed, Five or six pairs of feet 

 separated from each other by nearly equal intervals, the anterior 

 unguiculate, the posterior always furnished with large branchial 

 laminae directed longitudinally. Intestinal canal forming a loop, 

 which is generally double, in the thorax, and furnished in its 

 passage through the abdomen with a coeciform appendage. 



Genus. LYNCEUS, Mutter. 



[Chydorus, Leach, 1819. Alona, Camptocercus, Acroperus, Pleu- 

 roxas, and Peracantha, Baird, 1843. Alonella, Grapto- 

 leberis, Sarporhynchus, and Alonopsis, Gr. 0. Sars, 1862, 

 Rhypophilus, Schoedler, 1863.] 



Head projecting in a hood-like shape over the bases of the 

 anterior and posterior antennae, the former of which are nearly 

 or quite covered by it. Eye accompanied by a secondary eye- 

 spot, which is situated between it and the end of the rostrum. 

 Posterior antennae two-branched, each branch consisting of three 

 joints; one branch furnished with three, the other with four or 

 five geniculate and ciliate setae. Six pairs of feet ; the first in 

 the male furnished with a large hook-formed process used in seiz- 

 ing the female. Abdomen capable of being folded upwards- upon 

 the thorax, or of being stretched out in a line with it ; terminat- 

 ing in two strong claws, and having more or less numerous spines 

 articulated to the superior (i.e., dorsal) margin. Intestine form- 

 ing two convolutions in its course. Anal opening on the superior 

 margin of the abdomen, at some distance from its extremity, and 

 anterior to the row of marginal spines. 



No less than ten genera have been formed out of Lynceus, the 

 names of which are enumerated above. "When an attempt was 

 made by Dr. Baird to subdivide the genus, unable to find any 

 structural differences on which to base the character of the genera 

 he described, he relied mainly on the variations in the form of 

 the carapace. The result was unsatisfactory at the time, for 

 genera most certainly should be established upon differences of 



