11 



than the superior, flagelluni short, and, as a rule, only Inarticulate. Mandibles 

 of various structure in the several genera, but always without palps. Anterior 

 maxillae with only a single slender masticatory lobe; posterior ones quite 

 rudimentary, forming simple rounded lobes. Maxillipeds coalesced at the base, 

 epignath generally narrow, falciform. Chelipeds, as a rule, strongly built and 

 closely applied to the oral area, issuing from the posterior part of the cephalo- 

 some with a broad base, carpus generally broad and compressed, hand some- 

 times rather dissimilar in the two sexes. Second pair of legs not very different 

 from the succeeding ones, being rather small and ambulatory in character. Pleo- 

 poda, as a rule, very small, with the rami lamelliform and incurved, sometimes 

 in female rudimentary or quite wanting. Uropoda not much elongated, simple 

 or biramous. 



Remarks. — This family may be easily distinguished from the preceding- 

 one, both as regards the outward appearance of the body, and the structure of 

 the several appendages. It comprises rather a large number of genera, amounting 

 to about 15 in all. These genera are chiefly characterised by the structure of the 

 mandibles, partly also by that of the superior antennse, the legs and the several 

 appendages of the metasome. As to habits, the greater part of the species — 

 perhaps all — seem to be tubicolar in character, constructing for themselves abodes 

 of mud, into which they may wholly withdraw their bodies. They all, moreover, 

 exhibit this peculiarity, namely, that on reaching the surface of the water, they 

 remain floating, without being able to reimmerge their bodies, whereby the dis- 

 covery of the generally very small and inconspicuous specimens is essentially 

 facilitated. On placing some muddy clay taken from greater depths, in a shal- 

 low vessel, and stirring up the mud, they will very soon appear floating on the 

 surface like small white pins, and may easily be taken up for a closer examina- 

 tion. To the Norwegian ' fauna belong 11 different genera, to be described below. 



Gen. 1. TanaiS, M.-Edw., 1829. 



Syn. Orossurus Rathke. 



Generic Characters. — Body not much elongated, but with the cephalosome 

 rather tumid and provided with distinctly defined ocular lobes. Metasome only 

 composed of S^segments. Eyes well developed. Superior antenna? of similar 

 structure in the two sexes, 3-articulate, with a very small knob-like terminal 



