THE OSTEACODA. • 249 



joint swollen on the ventral border, diminishing suddenly to a narrower tip, the end 

 rounded and carrying an insignificant spike ; a few fine spines on the ventral border. 

 Antenna 1. with the principal bristle of female character. Antenna ii. without hooks, 

 the central bristles as in the later stage : there are two basal bristles, the one very tiny, 

 the other fairly long. 



Female (Mean, 1-60).— Shell slightly more elongate than in Stage II., but retaining 

 the projecting opening of the right asymmetrical gland and the postero-dorsal glands. 

 Frontal organ thicker than the stem, but incompletely segmented from it, tapering 

 to a blunt tip, carrying a few fine spines ventrally. Antenna i. with a hairless dorsal 

 bristle (accidentally omitted in fig. 200). Antenna ii. with the shorter central bristle 

 about two-thirds of the other ; both hairless. 



Stage IV. 



Male (Length, 1-1). — Shell with postero-ventral angle more rounded than in 

 Stage III., posterior border at a slightly obtuse angle to the dorsal border, ventral 

 ■border nearly straight ; opening of right asymmetrical gland prominent, postero-dorsal 

 glands just recognisable. Frontal organ short, slightly thicker than the stem, 

 unsegmented, spineless. Antenna ii. Avith one fine basal bristle (? two) ; the shorter 

 central bristle half the length of the other, both hairless. 



Female (Mean, 1-04).— Shell with postero-ventral angle more rounded, postero-dorsal 

 angle more obtuse, and ventral border more convex than in later stages ; the highest 

 point of the shell lies at about the middle of its length. Opening of the right asym- 

 metrical gland projecting, but postero-dorsal glands not recognizable. Frontal organ 

 elongate, simple, the terminal joint not segmented from the stem, ending bluntly ; one or 

 two fine spines on the ventral surface. Antenna 1. without dorsal bristle. Antenna ii. 

 ■with central bristles as in the male. 



Stage V. 



Female (Mean, OwO).— Shell sharply convex ventrally; the opening of the right 

 asymmetrical gland is prominent, but does not project so much as in the later stages. 

 The left lateral gland is already distinguishable, but very small. Frontal organ 

 simple, short, blunt ; the future terminal joint slightly thicker than the stem, constricted 

 distally. Antenna ii. with a single hairless bristle of medium length. 



The specimens at 0-6 mm. may perliaps belong to an earlier Stage VI., but their 

 determination is naturally rather uncertain. In them the opening of the right asym- 

 metrical gland resembled that of macromma (MuUer, xvii. 12), and was very high up, at 

 nearly half the height of the shell. 



CoNcncECiA iiOTUNDATA, MuUer. 



(Plates 23, 24. figs. 205-224.) 



According to Dr. Miillcr, the shells of this species exhiluted a remarKable variation 



in shape, the height being anything from 41 to 57 per cent, of the length. Now in all 



other Halocypridaj which I have handled the shell-shape is very fairly constant, and the 



general contour gives one of the most reliable specific characters, but its diagnostic 



