LYSIANASSIDAE 29 



From borealis it differs in the much stouter palp of the maxilliped, the slightly more 

 broadly rounded postero-inferior angle of pleon segment 3, and the (vertical) depth of the 

 excavation on side-plate 4 being equal to the (vertical) depth of the backward process 

 (in borealis, Sars, 1895, pi. xl, fig. 2, the former is greater than the latter, if the figure is a 

 true side view and the lower parts of the side-plates are not foreshortened). 



Distribution. 'Gauss' winter station, 385 m. 



Genus Shackletonia, Brnrd. 

 Barnard, 193 1, p. 425. 



Body robust. Side plates deep, 1st deeper than 2nd and 3rd, 4th large, deeply ex- 

 cavated, 5th bilobed, posterior lobe deeper than anterior. Telson deeply cleft. Antennae 

 (immature) short, 2nd and 3rd peduncular joints of 1st antenna very short, accessory 

 flagellum nearly as long as flagellum. Mouth-parts rather prominent. Epistome evenly 

 convex in front, passing into upper lip without any intervening notch or groove. 

 Mandible elongate, cutting edge straight, molar slight, conical, palp inserted in middle 

 of trunk just behind molar. Lobes of lower lip subacute. First maxilla slender, outer 

 lobe with very oblique distal margin set with six strong recurved hooks, palp 2-jointed, 

 distally narrowing to subacute apex. Second maxilla slender, inner lobe shorter than 

 outer. Maxilliped with inner plate small, slender; outer plate large, margin entire and 

 unarmed; palp moderate, 4-jointed. First gnathopod simple. Second gnathopod 

 minutely chelate. Peraepods 3-5 with 2nd, 4th and 5th joints strongly expanded. 

 Uropods 2 and 3 with peduncle stout. Accessory branchiae one on each of segments 2-5, 

 two on segment 6. 



Remarks. This form has characters of both Acidostoma and Phoxostoma. The mouth- 

 parts show the peculiar hook-like spines on the 1st maxilla only found elsewhere in 

 Acidostoma, and which are possibly adaptations to a particular diet. On the other hand 

 the palps of maxilla 1 and maxilliped show no degeneration. The development of the 

 accessory branchiae is exactly like that of Waldeckia obesa and raises the question as to 

 what systematic value these structures possess. 



Named in commemoration of the exploits of the late Sir Ernest Shackleton in the 

 Antarctic regions. 



Shackletonia robusta, Brnrd. (Fig. 3). 



Barnard, 193 1, p. 425. 



Occurrence: 1. St. 123. South Georgia. 1 juv. 12 mm. 



2. St. 170. South Shetlands. 1 immat. 28 mm. Type. 



Description. Body robust, tumid in middle as in Waldeckia obesa. Integument 

 indurated, with scattered punctures extending over the peraeon, pleon, side-plates and 

 2nd joints of peraeopods 3-5. 



Head with antero-lateral angle rounded. Eyes large, reniform, wider below than 

 above, dark. 



