16 PROF. M. M. HAETOO ON THE 



VI .-IX. Anterior Thoracic Appendages. Swimming-Feet, Oar-Feet* (PI. I. figs. 8, 9). — 

 The first four pairs of thoracic appendages are biranious swimming-feet, which have given 

 the name to the order. They resemble one another in so many points that the 

 description of one is that of all, save in slight details. We shall therefore commence with 

 the description of the anterior or first thoracic limb. It is flattened from before back- 

 wards, with a thicker protopodite, composed of a coxopodite, united across the middle line 

 with its fellow by a median coupler, and a basipodite ; the latter bears the two rami (endo- 

 podite and exopodite). 



Coxopodite transversely oblong, bevelled off at inner angle, where it bears a long 

 plume t ; above this, joined to the coupler (curved), distal edge bearing a row of fine 

 teeth ; another row traverses the middle of the posterior face, and is continued across the 

 coupler. Its outer edge is fringed with long setae. 



Basipodite oblong, much shorter (from above downwards) than coxopodite, and not 

 extending inwards beyond the bevel of the latter. Distally it is excavated on the outer 

 side bv a concave bevel for the insertion of the exopodite, external to which is a long 

 plume, while in the middle of this edge a short process, on which is inserted the endo- 

 podite between an (internal) plume and an external tooth. The inner edge is rounded at 

 the angle and finely fringed with seta?. 



Fndopodite. — First joint squarish, convexly tapered at insertion ; distal edge finely 

 toothed ; inner edge bearing beyond its middle, on a step-like indentation, a long plume, 

 above which is a strong tooth ; outer edge finely setose, produced at distal angle into a 

 sharp tooth. Second joint stouter, half elliptical ; distal edge finely toothed ; inner edge 

 bearino- on successive step-like processes two plumes, setose, proximal to the first, and 

 endin"" at distal angle in a sharp tooth ; outer edge as in first joint. Third joint elliptical, 

 truncate at both ends ; distal edge bearing a strong saw between an (internal) plume and 

 an (external) strong tooth ; inner edge bearing three plumes ; outer finely setose. 



Exopodite rather shorter than endopodite, and from its more proximal insertion reach- 

 in " little beyond the base of its third joint ; resembling it in the general form of its 

 joints, which are, however, broader ; and the third is longer, almost triangular, with the 

 base proximal. 



First joint setose on inner edge, with a single plume at distal angle ; outer edge setose, 

 with a saw between two teeth (i. e. proximal and distal) at distal angle. 



Second joint like first. 



Third joint, distal edge bearing two plumes; inner edge not fringed, bearing two 

 plumes ; outer edge bearing distally three distant teeth, and in the intervals a saw. 



The other three pairs of limbs are similar to the first, but more elongated. The third 

 is the largest and stoutest, the fourth the most elongated and slender. In the fourth the 

 internal plume of the basipodite is replaced by a strong tooth, and, as in the second and 

 third, the fringe along the outer edge of the protopodite is finely serrated instead of being 



* I regard the oar-feet as flexed when bent backwards and upwards ; extended when bent forwards, 

 t All the plumes of the limbs are pinnately setose on the transverse plane only. 



