LMcMURRICHJ 



NOTES ON SOiME CRUSTACEAN FORMS 



55 



nules (Fig. 9 A) being being uniramous structures consisting of a 

 somewhat enlarged basal joint, followed by three ( ?) narrow ring-like 

 segments and terminating in an elongated digitiform portion. The 

 apex of this terminal joint bears four setae, two of which are many- 

 times the length of the terminal joint, while the other two, which 

 flank the long ones, are about the same length as that joint. The 

 antennae and mandibles seem to have practically the same form, the 

 description that follows being that of the mandible. It is a biramous 

 structure (Fig. 9B) with two basal joints. The inner ramus is 2- 

 jointed and is produced on its inner side into a strong slightly curved 

 masticatory spine, as is also the distal basal joint. The proximal 

 joint of the inner ramus also bears a rather short seta and the terminal 

 joint bears two, also rather short. The outer ramus is five-jointed, 

 the terminal joint being very small and bearing a single seta; the 



Fig. 9. Hansen's y larva. A, first antenna, B, second antenna of Stage II. 



second, third and fourth joints bear setae at their inner distal angles, 

 those of the third and fourth joints being long, about twice as long as 

 that of the terminal joint, while the one on the second joint is much 

 shorter, being only about half the length of the terminal seta. 



Stage III. No examples were found of any stages older than the 

 second, but within the carapace of this stage important changes take 

 place and some of the examples showed contained larvœ which indi- 

 cated the characteristics of the succeeding stage. 



The most striking feature of these larvae is the replacement of the 

 original carapace by a shield (Fig. 10) rounded in front and produced 

 posteriorly into a strong angle on either side, the whole having a 

 remarkable similarity in outline to the "shell" of such a form as 

 Apus. The shell was apparently homogeneous in texture, no indi- 

 cations of either plates or a dorsal hinge being visible. The larva is 

 divisible into three regions the anterior of which bears the three pairs 

 of naupliar appendages. No segmentation could be seen in this region 

 even in stained preparations (Fig. 10). The appendages had the 



