100 



THE VOYAGE OF H.M.S. CHALLENGER. 



very youngest sliells (r-it), and in these the surface-ornament, though much more delicate 

 than in the adult, is sufficiently obvious ; this character becomes increasingly distinct 

 with the age of the animal, until in what appear to be the very oldest examples {j, v) the 

 reticulations have become very massive and rounded by constant depositions of calcareous 

 substance, while the intervening fossae are proportionally deepened. It is not uncommon 

 to find the sculptured ornament of Ostracoda filled up and partly obliterated in old age ; 

 possibly this might be the case in still older sjoecimens of Cythere dictyon than those 

 which have come under my observation, btit at present I have seen no trace of the obli- 

 terating process in this species. The tapering form of the valves in the earlier stages of 

 growth is plainly shown in the plate, as also the absence or comparative feebleness of 

 spinous armature. The adult varieties do not call for much remark ; the spinous termina- 

 tion of the ventral ridge is seen in figures f, g, and ^, and a marked difference of contour 

 is apparent in the dorsal views (6, ^); this may perhaps be dependent on growth, or 

 possibly on distinction of race. I long hesitated as to whether or not the forms shown in 

 figures y and v should be considered to belong to Cythere dictyon. The chief points of 

 divergence are the very convex ventral margin, the contracted and strongly-indented 

 dorsum, and (in figure i') the marked projection of the infero-posteal angle; I believe, how- 

 ever, that these conditions are mere exaggerations of characters which belong to the 

 species, and which may be found developed with variable degrees of distinctness in 

 difierent examples. 



Cythere dictyon occurred in a great number of the Challenger dredgings, — mostly in 

 those from deep water, — in some of which it was the most abundant species. The following 

 is a list of the localities : — 



Off Culebra Island, West Indies, . 

 Lat. 35° 35' K, long. 50° 27' W., 



