Amphiascus thalestroides, G-. 0. Sars, n. sp. 



(Suppl. Pi. 17). 



Specific Characters. Female. Body comparatively slender and gradually 

 tapered behind, resembling in shape somewhat that in certain species of the 

 genus Parathalastris. Rostrum not much prominent, triangular in form, with the 

 tip somewhat blunted. Urosome almost as long as the anterior division, and 

 having the segments very sharply marked off from each other, the last one rather 

 small. Caudal rami quadrangular, broader than they are long and spinulose inside, 

 apical seta 1 unusually strong and dark-coloured, the inner medial one, as usual 

 the longest and gradually thickened in its proximal part. Anterior antennae of 

 moderate length and composed of 8 joints, the first 2 much the largest, the 2 

 succeeding ones about equal-sized, terminal part rather slender, considerably 

 exceeding half the length of the proximal one. Posterior antennae with the middle 

 joint of the outer ramus imperfectly developed and without any setse. Maxillae 

 with the masticatory lobe unusually strong and armed with a limited number of 

 coarse claw-like spines. Oral parts otherwise normal. 1st pair of legs with both 

 rami distinctly prehensile, the outer one rather short, not nearly attaining the 

 length of the 1st joint of the inner, its middle joint somewhat dilated and oval 

 in form, last joint lamellar, rounded, and armed with 4 curved claws succes- 

 sively increasing in length distally, and at the inner corner with a slender seta; 

 inner ramus with the 1st joint linear in shape and carrying near the end inside 

 a well-developed plumose setae, the 2 outer joints of larger size than in the pre- 

 ceding species, and each provided inside with a small seta, last joint being larger 

 than the preceding one and carrying on the tip 2 strong unequal claws accompanied 

 inside with a thin seta. Natatory legs well developed, with the full number of 

 seta3, middle joint of inner ramus acutely produced at the outer corner. Last 

 pair of legs rather large, distal joint broadly cordiform and edged with 6 rather 

 strong, dark-coloured setae, one of then, however, attached to the conically pro- 

 duced tip of the joint, thinner than the others; inner expansion of proximal joint 

 comparatively short, triangular, not nearly extending to the middle of the distal 

 joint, marginal setae 5 in number, the middle one the longest. 



Colour not yet ascertained. 



Lenght of adult female about 1 mm. 



Remarks. This is one of the larger species of the genus, and, like the 

 preceding one, belongs to the section in which both rami of the 1st pair of legs 

 are pronouncedly prehensile. It may easily be recognised both by the general 

 form of the body and by the structure of the 1st and last pairs of legs. 



