THE OWTBACODA. 253 



a single vow uuless viewed directly from above. Antenua ii. as figured for Stage II. ; 

 tlie shorter central bristle about two-thirds of the longer; the latter with a few very 

 long hairs ; there are two basal bristles, the one more than twice the length of the 

 other, both slender and hairless. 



The exact shape of the saw-teeth is difficult to make out owing to their minuteness 

 and high refraction. They appeared to have rather the shape given in fig. 238 than 

 that shown in Midler's drawing (xxii. 25). The sub-cuticular teeth shown in his figure 

 appeared in one specimen at Stage II., and probably indicated an approaching moult. 



Female of this stage not observed. 



'a^ 



Stage II. {spliiirostrls stage). 



Male (Mean, 0-93). — This is hardly distinguishable from Stage I., but (1) the posterior 

 border of the shell is rather straighter ; (2) the teeth ou the armature of the principal 

 bristle of antenna i. were about 8-11 pairs of saw-teeth and about 8-9 pairs of spine- 

 teeth ; (3) the frontal organ was rather slenderer, not much thicker than the stem. 



Eemale (Mean, I'lO). — Shell with a sharply curved posterior border, and a fairly 

 prominent opening to the right asymmetrical gland; no postero-ventral angle. The 

 ventral border is very slightly arcuate, the highest point well behind the middle of the 

 shell-length; tapering gradually forwards. Frontal organ of very larval appear- 

 ance, spineless, unsegmented, only slightly swollen anteriorly, terminated acutely. 

 Antenna ii. with the shorter central bristle about two-thirds the len"-th of the 

 longer, the latter with a few fine short hairs at its base. No basal bristles. 



The female is difficult to identify, owing to the fact that the frontal organ lias the 

 characters (or, rather, absence of positive characters) which one has learnt to associate 

 Avith larvcG of eai'lier stages in other species (smoothness, transparence, symmetrv of 

 dorsal and ventral borders, thin wall, absence of segmentation, &c.). But as some 

 females carried comparatively large ova (0-08 mm. diam.) they were uot far from 

 maturity. 



Stage III. 



Male not observed. 



Female (Mean, 075). — Shell with the posterior border straighter than at Stage II. ; 

 no postero-ventral angle, ventral border slightly convex. Frontal organ as in Sta"e II., 

 but shorter. Antenna ii. Avith two central bristles as in Stage II., but hairless. 



CONCHCECLA TYLOUA, MiiUcr. 



A single male specimen of 2'8 mm. in fau' preservation agreed with Midler's figures 

 and description. On the principal bristle of antenna i. there seemed to be about 57 pairs 

 of leaf-like structures (which at first look like very fine spines), distal of these are 

 3 or 4 short spines directed distally. Antenna ii. carried two basal bristles (Miiller 

 figures one only), the one about two-thirds the lengtli of tlie other. 



.\. ])air of empty shells which carried the characters of this species was also taken ; 

 their length was +27 mm. 



42* 



