234 DE. G. H. FOWLER — BISCATAN PLANKTON: 



Ventral border convex ; tbe shell is highest about tbe middle of the length. Erontal 

 organ very short, of tbe form drawn by Miiller (xiii. 20) or as in figure 59. Antennse 

 i. and ii. as di-avvn or described by Miiller (xiii. 21, 22, 26). 



Female (Mean, +1'12). — Shell of the same character as in the male, except that 

 on the posterior border the upper part is generally more deeply concave, tbe lower more 

 sharply convex. Tbe ventral border somewhat more tapered than in tlie male. 

 Frontal organ and Antenna i. as drawn by Miiller (xiii.* 10, 11, 24), the former 

 projecting only a short distance beyond the latter (unlike spinifei-a and 'procera). 

 Antenna ii. without basal bristles, with two short hairless central bristles, the one 

 about twice the Jength of the other. 



The extent of the concavity of the posterior border is more or less impressive, 

 according as the spines are more or less developed ; but the convexity is always greater 

 in the female than in the male. 



Stage III. 



Male (Mean, iO'9). — Shell much as in Stage II., but slightly more tapered an- 

 teriorly t. Frontal organ unsegmented, the terminal part swollen, ending bluntly. 

 Antenna i. with the principal bristle of female character. Antenna ii. as in the female, 

 except for the presence of a single basal bristle. 



Female (Mean, ±0'86). — Shell witli the posterior border as in Stage I., but the 

 ventral border is more convex, and the shell therefore higher in proportion to the length. 

 Frontal organ very larval in charactei% only slightly swollen terminally. Antenna ii. 

 as in Stage II. 



It is very difficult to distinguish these young specimens at first from Stage III. of 

 spinifera. But the frontal organ, which in elegans only just projects beyond anteuua i. 

 extends in spinifera a long way beyond it. Further, spinifera has a well-marked 

 shoulder-ridge ; and was not observed at this stage to carry a spine, whereas elegans 

 generally does. The ventral border is more convex in elegans, straigbter in spinifera. 

 The characteristic openings of the marginal glands in elegans., figured for Stage I. by 

 Miiller (xiii. 19), are very imperfectly developed at this and earlier stages. 



Stage IV. 



Shells (c? 2 Mean, +0"6) of both male and female as in their respective sexes at 

 Stage III., except that tbe ventral border is more convex, and the shell is fuller in 

 front, so that tbe highest point lies a little in front of the middle of the length. No 

 postero-dorsal spine was observed at this stage. The male was distinguishable fixmi 

 the female only by the rudiments of the penis. Cephalic organs as in Stage III. 

 I'emale. 



* Figure 29, between figs. 21 and 25 on this plate, should apparently be 23, and of a male. 

 t Tbe specimen drawn in fig. 60 bad the spines rather better developed than that of fig. 58 ; hence at first the 

 postero-dorsal concavity appears to be more stronglj- marked. 



