THE OSTEACODA. 



241 



briofly by Miiller ; tbcy are : (1) the extent to which the shell-sculpture is recognisable, 



(2) the numlier and arrangement of the teeth on the principal bristle of antenna i., and 



(3) the size of the shell. The first of these three points seems to be quite unreliable for 

 diagnosis in formalin specimens : of two otherwise absolutely similar specimens from the 

 same haul, the one would show well-marked sculpture, in the other it would be barely 

 visible ; this was noticeable in other species also. The other two diagnostic points might 

 be (and in the case of the two larger " species " they probably are) merely expressions of 

 different ages or stages of the same species. Miiller furnishes the following particulars :— 



By size and by number of teeth my specimens were ctenoj)liora ; in every other 

 respect they agreed with Miiller's description of lorieata, var. tijpica. If, as I believe, 

 these are merely the last two stages of one species, the older name lorieata claims 

 priority. 



Stage I. [cteno^ohora stage). 



Male (Mean, 231). — Shell more tapered anteriorly, and with a more marked 

 shoulder-ridge than in macfna, posterior border nearly straight and at riglit angles to the 

 dorsal border, postero-ventral asymmetrical gland prominent, ventral border arcuate ; 

 the shell not so liigli in front of the arcuation as behind it, the anterior border beginning 

 to taper upwards immediately after the arcuation. Frontal organ much as in magna, 

 about as thick after the central constriction as before. Antenna i. : the toothed and 

 pi'oximal toothless parts of the pi-incipal bristle subequal, the distal toothless part longer. 

 Teeth about 30-32 pairs, nearly all ecj^ual and nearly equidistant at all points. The 

 principal somewhat longer than the accessory bristles, which carry a few minute teeth. 

 Antenna ii. with the inner branch as drawn by Miiller (xxii. 17), but the longer central 

 bristle is often (not always) hairless, and the larger basal bristle is longer and slenderer 

 than (owing to foreshortening) appears in this figure. The process on the inner side of 

 the proximal part of the hook appears to be constant, and not to occur in magna. 



Female (Mean, 2-5S). — Shell with fairly marked shoulder-ridge. Posterior border 

 beginning above with a slight concavity, then markedly convex, projecting further 

 posteriorly than in the male. Ventral border fuller than in the male behind the arcuation, 

 so that the highest point of the shell lies well behind the middle of tlie length. Other- 

 wise as in the male. Frontal organ and Antenna i. as drawn by Aliiller (xxii. 3). 



* Figure without rostrum, 1-4. 

 t Figure without rnstium. 1-7. 



