254 Dli. G. H. rOWLEE— BISCATAN PLANKTON : 



CONCHffiCIA ZETESIOS, sp. 11. 



(Plate 25. figs. 247-253.) 



Ouly I'euialcs of this iiu described form were tal^eu by the ' llesearcli,' rej^reseuting 

 two stages and iu veiy small numbers. Tbe species obviously belongs to the inaf/ua 

 group. While the shell-contour to some extent resembles that of ' ■uiacrochelra,' its 

 frontal organ and the slender longer bristle of the inner joint of antenna ii. are very far 

 from the magna-nmcrocheira type; nor can it be fitted into the lengths which have been 

 Avorked out for that series. It is remotely possible that it may be a dimorphic partheno- 

 genetic form of magna, but iKU'thcnogenesis has not yet been shown to occur in the 

 Halocypridte (compare p. 308). 



Stage (?) I.* 



Eemale (Mean, 2-42)— Shell very foursquare, shouldcr-ridge slight; the posterior 

 border steadily convex ; the opening of the right asymmetrical gland rather high, that 

 of the left rather far forward ; no postero-ventral angle ; the ventral border very long, 

 markedly arcuate, generally so full anteriorly that the highest point of the shell is in 

 front of the arcuation ; the anterior border very bluff ; the rostrum so bent downwards 

 that its anterior face is at right angles to the dorsal border, and if produced would 

 nearly (or quite) make a tangent to the anterior border. Prontal organ very long; 

 the terminal joint imperfectly segmented from the stem ; the proximal half of the 

 terminal joint is rather thicker than the stem; the distal half is much thicker and 

 terminates in a blunt downwardly directed spine ; it carries a few spines on its dorsal 

 border only. Antenna i. with a very long dorsal bristle, the distal half of which 

 carries long fine hairs. Antenna ii. with a very low peg {Warze, Ilamillar-hocker), 

 devoid of basal bristles ; the longer central bristle is about twice the length of the 

 shorter and carries short hairs ; the shorter also in some cases has hairs. 



Stage (?) II. 



Female (Mean, 1*5). — Shell with a more convex posterior border; the anterior 

 part of the ventral border is fuller, so that the highest point of the shell is far in front 

 of the arcuation ; the rostrum is bent at first downwards, then inwards ; in other 

 respects the shell is as in the later stage. Frontal organ of the same general type as 

 in the later stage, but less swollen and spineless. Antenna i. with a dorsal bristle, 

 shorter than in the later stage, and hairless. Antenna ii, as in the later stage. 



CONCHCECIA B. 



(Plate 25. figs. 254-257.) 



A single female from 22 b (750-500 fathoms), 1'7 mm. in length, was possibly 

 referable to the penultimate stage of dorsotiiherculata. The general outline of the 

 shells agrees sufficiently with Miiller's figure x. 1, allowance being made for a small 

 difference between the sexes. The opening of the left asymmetrical gland is not nearly 

 so far forward as in clorsotuherculata, but is further forward than is normal in 



* The ovary was in all cases so iioorly developed, that it is possible thai the spocimeus were only semi-mature. 



