22 



G. O. SARS. 



[No. 1. 



successively in size anteriorly, becoming at last very slender 

 and elongate (see Pl. II, fig. 2). 



As to the muscnlature of the trunk, two sets of muscles 

 may be distinguished, the one dorsal, the other ventral, both 

 extending longitudinally. The dorsal muscles are very strong, 

 forming several layers, and pass as a rule rather regularly 

 from one segment to the next. The ventral musculature, on the 

 other hand, is chiefly represented by only a single very slender 

 muscle on either side, extending along the whole ventral side just 

 above the insertion of the legs and posteriorly dividing into a 

 number of separate bundles, the posterior of which enters the 

 tail anteriorly. 



The limts of the trunk, generally termed legs or branchial 

 feet, though with the present group of Phyllopoda not serving by 

 any means for locomotion, are invariably thirty-two or sixteen 

 pairs in number, each segment bearing one pair. They decrease 

 successively in length posteriorly, the first pair being the longest 

 and reaching almost to the free inferior edge of the shell, whereas 

 the posterior pairs become very small. As to structure, they are, 

 as in most other Phyllopoda, very delicate foliaceous organs, all 

 of them exhibiting a rather uniform appearance (see Pl. IV, figs. 

 7, 8, Pl. V, figs. 1, 2, 4). On each leg the following principal 

 parts may be distinguished (see PL VII, fig. 6): the main stem, 

 or endopodite (I— VI), the epipodite (ep), an( i the exopodite (ex), 

 the two latter originating from the outer side of the former. 



The endopodite consists of six imperfectly defined segments, 

 each of which is produced on the inner side as a rounded seti- 

 ferous lobe. The uppermost lobe, issuing from the first or coxal 

 segment (Pl. VII, fig. 6, m, Pl. V, fig. 3), projects considerably 

 more than the others, and is also more strongly chitinized, 

 exhibiting a rounded triangular form. It has at the tip three 

 rather strong biarticulate and densely citiated setæ, the upper- 

 most of which is the longest and more or less geniculate on 

 the middle; on either side of these setæ two spines are affixed, 

 those on the upper side being the strongest. Moreover, a dense 

 series of very delicate curved bristles extends along the edge of 



