22 G. O. Sårs. 



valves now occupy only a comparatively small part of the 

 shell, and their edges, forming the 1st line of growth, are 

 concentrically encompassed by the 4 other lines, which all, 

 like the free edges of the valves, are densely setiferous. 

 The form of the shell is still somewhat more elongated than 

 in the 4th stage, more approaching that in the adult animal, 

 though the umbonal part appears far less prominent. 



The enclosed animal (not drawn in the figure), which 

 now exhibits a clear yellowish orange hue, has developed 

 its appendages more fully, the antennulæ being considerably 

 more elongated, and each of the rami of the antennæ having 

 become 8-articulate. The branchial jlegs have increased in 

 number, 12 pairs being now distinctly developed, and behind 

 them there is, moreover, a slight trace of 2 other pairs in 

 process of formation. The tail does not differ from that in 

 the preceding stages, except by a somewhat increased number 

 of denticles on the concave edge of the terminal plates. The 

 cæcal appendages of the intestine have now divided into 

 numerous lobes, and exhibit a clear yellowish hue. 



Ninth postlarval stage. 



(PL IV, fig. 2). 



The length of the shell in this stage has increased to 

 2,25 mm., the height being 1,55 mm., and its form is now 

 rather similar to that of the adult animal, though some- 

 what more compressed. The lines of growth are 8 in each 

 valve, being all, except the 1st, like the free edges of the 

 valves, fringed with bristles, which, however, are shorter 

 and more densely croAvded than in the stages previously 

 described. The 1st line of growth now only encompasses a 



