BELONGING TO THE GENEEA BEADY A AND ECTINOSOMA. 433 



antennules and broadly subquadraugidar form of the llftb. pair of thoracic feet, the apical 

 spines of which are all of nearly equal length, are characters by which it can be readily 

 distinguished. 



EcTiNOSOMA PYGM^UM, sp. n. (PI. 36. figs. 15 and tl ; PL 37. figs. 5, 20, 39, 43 ; 

 PL 38. figs. 4, 26, 31, 55.) 



DescrijjtioH. Length "33 mm. {-f-^ of an inch). Seen fiom the side the thoracic 

 portion of the body is moderately stout, with the dorsum considerably arched, but the 

 abdomen, Avhich is comparatively narrow, is only slightly tapering ; rostrum prominent 

 (PL 36, fig. 15). 



Antennules 6-jointed, short, moderately stout, gradually tapering to the apex and 

 furnished with numerous hairs ; the proportional lengths of the joints are nearly as 

 sliOAvn in the formula : — 



No. of the joints : 1.2.3.4.5.6 



Proportional lengths : 6 ^34222 ' 



Antennic larger than the antennules ; the secondary branch is composed of three nearly 

 equal joints, but tlic middle one is slightly shorter than the one on either side (PL 37. 

 fig. 5). Mandibidar palp well developed; basal joint large, with two plumose apical setae ; 

 the subapical branch is much larger than the marginal one ; two elongate teeth spring 

 from a notch near the middle of the inner margin of tbe mandibles, and reach to the 

 trimcate and slightly-toothed apex (PL 37. fig. 20). 



Anterior and posterior foot-jaws somewhat similar in structure to those of Ectinosoma 

 Sarsi, but very small (PL 37. figs. 39 and 13). The first four pairs of swimming-feet 

 are also somewhat similar to that species, but are more slender ; the marginal setoB are 

 plain, the first pair want the transverse rows of small spines possessed by those of 

 Uctinosoma Sarsi, and the outer branches of the fourth jmir are proportionally longer 

 (PL 38. figs. -1 and 26). The fifth pair are small and furnished with elongate fusiform 

 spines, which become extremely slender towards the extremity ; the secondary joint, 

 Avhich extends considerably beyond the inner produced portion of the basal joint, is 

 irregularly trilobed, and each lobe forms the base of a s})ine ; the two outer spines are of 

 nearly equal length, but the inner one is scarcely half the length of the one next to it ; 

 the outer portion of the basal joint is produced into an elongate and very narrow 

 appendage bearing a slender apical seta (PL 38. fig. 31). 



Caiidal stylets very short, being scarcely equal in length to the last abdominal segment 

 (PL 38. fig. 55). 



Habitat. Firth of Forth, and in the vicinity of Port Erin, Isle of Man. 



Remarks. This is the smallest species of Ectinosoma known to us. The structure of 

 the secondary branches of the antennae and of the mandibles, together with the peculiar 

 fusiform sjnnes of the fifth pair of thoracic feet, appear to be sufiiciently characteristic 

 to distinguish it from any of the others described in this memoir. 



