230 



DISCOVERY REPORTS 



layer of the calcareous plates of the third stage a new layer is added. This new layer 

 differs in structure from the first layer, which again is different from the primordial 

 structure. In the figures this first layer of the plates is distinguished from the primordial 



Fig. I. Scalpellum gibberum. a. Metanauplius (total length 1-09 mm.), b. Pupa just attached (total 

 length 1-23 mm.), c. Pupa with primordial valves, lateralia and dorsal scales of peduncle developed 

 (total length 1-25 mm.), d. Somewhat older stage (total length 1-23 mm.), e, f. Young specimens (total 

 lengths 1-23 and 1-52 mm. respectively). 



valves. In ho other species have I seen any differences in the structure in the first and 

 later layers of the laterals ; this fact does not seem to be of any phylogenetic importance, 

 although I have thought it well to mention it. The rostrum and rostro-Iaterals appear in 

 the fourth stage but, like the laterals of the third stage, they have only one layer. 



