SCALPELLUM 231 



In the fifth stage (Fig. i, e) the pupa valves have been thrown off, and new calcareous 

 layers have been added to all the plates. Thus the upper, inframedian and carinal laterals 

 have three layers, but the rostrum and rostro-laterals, which appear at a later stage, have 

 only two. In stages three to five the four dorsal scales are the only scales developed on 

 the peduncle. The structure of these scales is the same as described for the laterals. 

 They have in the third stage one layer, in the fourth two, and in the fifth three. 



In the sixth stage (Fig. i,/) the tentacle-like processes at the apex of the capitulum are 

 more distinct than in the preceding stage. The capitular valves have additional layers and 

 a shape more like the fully grown stage. The corners between the margins of the plates 

 are now more distinct than in the fifth stage. Thus the upper latus is now quadrangular, 

 the inframedian latus is pentagonal, and the rostral latus, carinal latus, and the rostrum 

 are quadrangular. The umbo is central in all plates except the carinal latus. In the last- 

 mentioned plate the umbo is first central (Fig. i, d), but is later situated at the carinal 

 margin. The peduncle is more developed, and new peduncle scales begin to appear 

 between the first scales and the lower lateralia. 



In the seventh stage (Fig. 2, a) the prehensile antennae of the pupal stage are still present. 

 On the capitulum one can study the further changes in the position of the umbo and 

 the shape of the valves. The umbo of the carina is further removed from the apex. In 

 the upper latus the umbo becomes nearer to the apex, for the lower part of the plate is 

 more developed. In the rostrum the umbo is sub-apical, in the rostral latus the umbo 

 is situated near to the upper rostral corner, and in the inframedian latus the umbo is 

 moved from a central to a sub-central position. In the carinal latus the umbo is placed 

 as in the seventh stage. The tentacular processes have nearly disappeared. In the upper 

 part of the peduncle new scales are visible. 



In the eighth stage (Fig. 2, b) the prehensile antennae are totally lost, and the primordial 

 valves have almost disappeared. The carina is angularly bent with the umbo above the 

 middle. In the rostral latus the umbo is situated in the upper rostral angle, and 

 in the inframedian latus the umbo is nearer to the basis. In other valves as in the 

 eighth stage. 



In the ninth stage (Fig. 2, c) the valves are close in shape to those of the fully grown 

 stage, but some small differences exist. The occludent margin of the tergum is straight. 

 The umbo of the carina is as in the eighth stage, but the lateral parts are more developed. 

 The upper latus is transversely elongated, with an upper secondary part very distinct. 

 The rostrum is quadrangular with a central umbo, and the visible part is triangular. The 

 inframedian latus has now a basal umbo. The carinal latus is nearly the same as in mature 

 specimens, with an umbo projecting behind the carina. In the peduncle a large number 

 of new rounded scales are visible. All scales of the peduncle tend to become of a more 

 rounded shape, but in the early stages, here figured, they are more transversely 

 elongated. 



The tenth stage (Fig. 2, d, e), which represents a fully grown animal, has a tergum 

 with a convex occludent margin, a carina with a central umbo, an inframedian latus with 

 a basal umbo and a more projecting carinal latus. The valves of the capitulum are 



