23 



forwards, greatest height quite behind and scarcely exceeding 2 /5 of the length, 

 dorsal margin straight and horizontal, ventral slightly arcuate and ascending 

 in front, posterior extremity broadly truncated, with the upper angle well 

 marked, lower rounded off; seen dorsally or ventrally, narrow oblong in outline, 

 tapering more in front than behind, greatest width behind the middle and but 

 little" exceeding 1 3 of the length. Rostral projections rather prominent and 

 somewhat vaulted above, subjacent sinus very wide, seen laterally almost rect- 

 angular. Surface of shell exhibiting a very delicate decussated sculpture; right 

 valve with the upper posterior corner produced in a spiniform point, in front 

 of which 2 recurved denticles of the dorsal edge are always found. Anterior 

 antennae scarcely reaching beyond the basal part of the posterior ones, and 

 exhibiting within their proximal part a number of dark yellow corpuscles, also 

 found in other species, and apparently visual in nature. Posterior antennae 

 with the basal part almost attaining half the length of the shell, outer ramus 

 7-articulate, inner ramus with 5 apical setae, one of them somewhat more 

 elongate than the others, which are all distinctly sensory. Frontal tentacle only 

 slightly dilated at the end and projecting a little beyond the anterior antennae. 

 Caudal lamellae with the deflexed spine of the anterior edge rater slender, 

 claws of moderate length, 7 in number on each lamella, and gradually dimi- 

 nishing in size proximally. 



Male of nearly same size as female and only sligtly differing in the shape 

 of the shell, though having the anterior part somewhat wider and the upper 

 posterior corner les prominent. Anterior antennae rather unlike those in female, 

 being much larger and divided into 4 well defined joints, the 2nd of which 

 is somewhat dilated at the base and filled with strong muscles acting upon 

 the 2 small' terminal joints, 3 of the apical appendages much prolonged, seti- 

 form, the other 2 sensory and very unequal in size, the anterior one bein very 

 small, the posterior elongated and extending backwards along the stem of the 

 antenna, outermost seta exhibiting, somewhat beyond the middle, a peculiar 

 dilatation in the form of a small oval disk finely striated radially and ap- 

 parently sucturial in nature. Inner ramus of posterior antennae with 2 of the 

 apical setae much elongated; prehensile hook well developed on the right 

 antenna, but much reduced on the left. Frontal tentacle with the extremity 

 conspicuously more dilated than in the female. Copulatory appendage of moderate 

 size, with the outer part slightly dilated and compressed. 



Shell in the living animal very transparent, pale straw-coloured, enclosed 

 body of a darker hue and in some places exhibiting a more or less conspi- 

 cuous reddish brown pigment. 



