1 '08. 59 



Acanthephyra (Systellaspis) debilis, A. M.-Edw. 



PL VI, figs. 1-15. 



Acanthephyra dehilis, Kemp, 1906 (1) {uhi syn.), PI. ii, 

 figs. 4-7. 



Systellaspis dehilis, Coutiere, 1906, figs. 1-4 (develop- 

 ment) . 



Acanthephyra gracilis, Hansen, 1908. 



The capture of further examples of this interesting form, 

 ranging from very young larvae up to mature specimens, pro- 

 vides material for the consideration of some of the features 

 of the development, and also allows a more complete specific 

 diagnosis to be drawn up. 



The rostrum is from one and a half to twice the length of 

 the carapace; it trends downwards at its base, but from its 

 middle point is again ascendant. On its basal crest it is 

 armed with three to five spines, two or three of which are 

 situated behind the posterior angle of the orbit ; the blade of 

 the rostrum is provided with from nine to twelve teeth above 

 and with eight to eleven below. The complete rostral for- 

 mula is usually found to be thirteen to sixteen above and eight 

 to eleven below. 



The carapace, measured in the middle line, is less than half 

 the length of the abdomen (excluding the telson) ; from the 

 rostrum a dorsal carina runs backwards, becoming obsolete at 

 about the middle line. The margin of the orbit is evenly 

 rounded as far as the supra-antennal angle (there is no pro- 

 minence representing the orbital spine as in A. purpurea) ; the 

 spine at the antero-lateral angle is sharp, but is not flanked 

 by any definite carina. 



All the ahdominal somites are dorsally rounded, wath the 

 exception of the third, which is strongly carinate and produced 

 posteriorly to a sharp spine projecting over about one-third of 

 the following somite. The posterior margins of the fourth 

 and fifth somites are also produced into short spines which are 

 laterally compressed ; the dorsal portions of the postero-lateral 

 margins of these i>wo somites are stTongly crenate in 

 mature specimens, less obviously in small examples. The 

 sixth somite is in small individuals about twice the length of 

 the fifth, in adults rather shorter. The telson is usually about 

 equal in length to the outer uropod and bears a rather peculiar 

 type of spinulation. The apex is very acutely pointed, and 

 immediately behind it are four pairs of spines, above which 

 there is a single pair of much stouter spines, which in some 

 cases reach more than half way towards the tip. Over the 

 base of each large spine a smaller one projects, which points 

 straight towards the apex and is not directed outwards like the 

 rest. Behind this terminal clust-er there are three to five pairs 

 placed in a dorso-laterai position. 

 An ocellus is present on the dorsal surface of the eyestalk 



