247 



as regards the structure of the oral parts, and it is therefore included here 

 within the last and most anomalous of the 8 subfamilies in which the Cythe- 

 ridae have been subdivided in the present Account. In addition to the typical 

 form described below, 6 other species, referable to this genus, have been 

 recorded by G. W. Muller, 3 of them from the Antarctic Ocean, the other 3 

 from the Gulf of Naples. 



136. Sclerochilus contortus, (Norman). 



(PI. CXII). 

 Cy there contorta, Norman, Ann. Mag. Nat. Hist. Vol. IX, p. 48, PI. II, fig. 15. 



Specific Characters. Female. Shell, seen laterally, oblong bean-shaped 

 somewhat higher behind than in front, greatest height not nearly attaining 

 half the length, dorsal margin .forming a gentle and quite even arch continuous 

 with both the anterior and posterior edges, ventral margin deeply sinuated in 

 front of the middle and gently convex behind, anterior extremity evenly 

 rounded off at the end, posterior obtuse, with no trace of a corner below; 

 seen dorsally, very "narrow oblong, with the greatest width not even attaining 

 1 /-i of the length, both extremities pointed and nearly equal. Valves semi- 

 pellucid, with the surface glabrous, inner duplicatures rather broad in front 

 and also well marked along the ventral face, marginal zone however com- 

 paratively narrow throughout and crossed by numerous short pore-channels, 

 edges clothed with fine hairs. Eye easily observable in the living animal, but 

 very soon vanishing in preserved specimens. Anterior antennae with the distal 

 segment of the basal part only slightly dilated, and provided with 2 slender 

 setse, one in the middle of the anterior edge, the other at the infero-posteal 

 corner, terminal part scarcely as long as the basal one, with the 1st joint much 

 larger than the other 3, which rapidly diminish in size, the last carrying on 

 the tip several extremely thin and slender setae partly connected at the base, 

 so as to present the appearance of a spurious apical joint. Posterior antennae 

 very robust, with the dividing suture of the penultimate joint located somewhat 

 below the middle, vesicle leading to the flagellum with each of the lappets 

 slightly bilobular at the end. 1st pair of legs with only a single curved spine 

 at the end of the basal joint, but with 3 juxtaposed delicate setae at the infero- 

 posteal corner. 



Male of rather smaller size than female, but only slightly differing in the 

 general shape of the shell. Copulative appendages with the basal part obli- 

 quely oval in shape, terminal part defined from the basal one in front by a 



