406 "THETIS'"' SCIENTIFIC RESULTS. 



Family ARCTURID^. 



ARCTURUS, Latreille. 



Many of the species of the genus Arcturus are very similar in 

 bodily contour and armature ; the various appendages appear to 

 afibrd the best characters whereby the species may be distin- 

 guished, and in this respect full use has been made of the relative 

 length of the body segments, joints of the antennae, and of the 

 legs. A glance at the text and the accompanying figures will 

 serve to show the value of the variation in the comparative 

 length of joints of the larger limbs. 



The position, number and character of the denticles or spines 

 are also of importance. In some species the armature consists of 

 a series of serrations ; in others, of distinct spines, generally fixed, 

 but occasionally mobile, especially near the extremities. 



ARCTURUS SIMPLICISSIMUS, sp. nov. 



(Figs. lUa-c.) 



Station 57. 



Adult male : — Body short, straight, and apparently without 

 the usual power of flexure between the fourth and fifth segments 

 of the peraeon. The superior surface is covered with a series of 

 tubercles and ridges ; the whole body, as well as the basal joints 

 of the antennse and legs, is more or less granulose ; some of the 

 granules are subspiniform. The cephalon bears four short, broadly 

 conical submedian spines — two on the frontal margin and two in 

 a transverse line with the hinder border of the eyes. 

 The segments of the peraeon bear a pair of low 

 submedian tubercles, and also a lateral pair which 

 tend to form longitudinal ridges. The segments 

 of the pleon exhibit a few low tubercles on each 

 side of the mesial line. 



The caudal shield has a pair of tubercles situated 

 in the middle of the distance between its insertion 

 and the extremity. 



The first and second segments of the peraeon are 



short and subequal in length ; the two combined 



are a little longer than the cephalon ; the third and 



fourth segments are equal in length ; the fourth is 



Second antenna;, slightly longer than the cephalon. 



Fig. 114a. Eyes large, dark brown, ijrominent. 



Inner antennae very short, about equal in length to the first 



joints of the outer; first joint one-third longer than broad; 



second equal to the first, but much narrower ; third joint about 



