THE OSTRACODA. 247 



Stage III. 



Male (Mean, 0"9). — Shell much as in Stage II., but the shoulder-ridge is not so 

 marked. Frontal organ simple, straight, unsegmented, the terminal joint not thicker 

 than the stem, ending shai'ply. Antenna i. with the principal bristle of female type. 

 Antenna ii. : the shorter central bristle is about three-fourths of the longer, the latter 

 may carry a few short hairs ; one (? two) short basal bristles. 



Female (Mean, 0'9). — Shell much as in Stage II., but the shoulder-ridge is not so 

 marked. Frontal organ still projecting far beyond the end of antenna i., simple, 

 unsegmented, the terminal joint rather thicker than the stem, the end tapered. 

 Antenna ii. as in Stage II. 



Stage IV. 



Male (Mean, 0' 65). — Shell with the height and length about equal; the ventral 

 border more sharply convex than in the later stages. Frontal organ ending bluntly, 

 simple, straight, still projecting well beyond the end of antenna i. Antenna ii. as in 

 fig. 181 (female). 



Female (Mean, 0-62). — Shell more sharply convex ventrally than in the male of this 

 stage, height rather more than half the length. Frontal organ still very long, the 

 future terminal joint hardly thicker than the stem, tapering to a point. Antenna ii. 

 with one long and one very short central bristle. 



Stage V. 



Female? (0-5). — Shell much as in Stage IV. Frontal organ long, but of the 

 simplest type, slightly swollen towards the end, ending bluntly. 



CoNCHCECiA PUSILLA, Miillcr, var. MAJOR, Miillcr. 

 (Plates 22, 23. figs. 184-187.) 

 Only six specimens of this form were taken. In supplement to Miiller s description, 

 it may be noted that it is at first extremely difficult to detect that the armature of the 

 principal bristle of antenna i. in the male consists of foliate plates and not of fine spines ; 

 their real form can only be seen if they are in exactly the right position. There were 

 about seven pairs, more or less in a double row, followed proximally by about seven 

 more (not pairs) more widely spaced, appearing as a single row but really set alternately 

 in a double row. As Miiller's figure of the shell (xvii. 36) was drawn from a " stark 

 verbogene" specimen, the right shell of an undamaged specimen has been figured. In 

 the female of 0-8 mm. the frontal organ was as drawn in Miiller's figure xvi, 35 ; in the 

 female of 06 as in his figure xvi. 36 ; there were two central bristles on the inner branch 

 of antenna ii., the shorter about three-fourths of the longer, l^oth very slender and 

 hairless. 



