232 DE. G. H. POWLEE — BISCATAN PLANKTON : 



The position of the opening of the right asymmetrical gland seems to he different in 

 the various figures ; this is mainly due to a dorsal or ventral tilting of the biconvex 

 specimens : its real position appeared to he at or just below half the height, except in 

 the very youngest specimens, where it is apparently higher. 



Stage I. (stigmatica stage). 



Male (about 1 mm.). — Shell vt'ith the shoulder- ridge very strongly marked*. The 

 posterior border begins as a nearly straight line making an obtuse angle with the dorsal 

 border ; at the opening of the right asymmetrical gland it becomes a steady convex 

 curve, which passes on without postero-ventral angle into the convex ventral border, and 

 then turns up rapidly as a flattened curve towards the rostrum. Frontal organ much 

 thicker than the stem, sometimes more flexed downwards than in fig. 31 : thickest 

 proximally, gradually tapered by depression of its dorsal border, the ventral border 

 being nearly straight; ending bluntly, spineless. Antenna i. : the principal bristle 

 carries 5-8 minute warts, very difficult to see. Antenna ii. : the right hook begins 

 with a very broad base ; becoming thinner, it commences to bend round with no trace 

 of an angle, is thicker at the highest point of the bend, and then tapers with a slight 

 S-curve, terminating in two divergent spines. The left hook, beginning with a thick 

 base, shows a distinct angle, and then tapers gradually like the right hook. One 

 proximal sense-tube is thickened at its base, and either dentate or spined. There are 

 two subequal basal bristles ; of the central bristles, the one is about twice the length of 

 the other ; all are hairless. (One of each was obscured by its fellow in fig. 33 ; compare 



fig. 37.) 



Female (about 0'95 mm). — Shell : the posterior border begins to curve almost imme- 

 diately after the postero-dorsal angle, and the curve is continued steadily till just below 

 the rostrum ; the antero-ventral border being more sharply curved and less flattened, 

 the female shell has a more rounded and less pointed outline than in the male. 

 Frontal organ showing a good deal of variation; always imperfectly segmented, 

 bluntly rounded or truncated, spineless, straight or very slightly bent. Antenna i. 

 with the distalmost sense-tube bifid, one branch being very short (fig. 47). Antenna ii. 

 with two central bristles, the one about twice as long as the other, both hairless. No 

 basal bristles. 



Stage II. {curta stage). 



Male (about 0'76 mm.). — Shell much as in Stage I., but a little higher for its 

 length. Frontal organ strongly flexed downwards, slightly curved, thickest distally, 

 terminating bluntly, spineless. Antenna i. with an armature of 9-12 1 blunt 

 points on the principal bristle. Antenna ii. : the right hook much as in Stage I., but 

 with a thinner base ; the left hook without an angle. One sense-tube is thickened at 

 its base, which is dentate or spined. 



Female (about 07 mm.). — Shell much as in Stage I. Frontal organ of the type 



* This is so at every stage observed, and will not be repeated. 

 t Muller records 8-13, but I bave not observed so great a range. 



