76 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 3 



PLATE 4 



Fig. 1. Stcphanut^yxts tiirris (Grev. and Arn.) Ralfs. Part of a chain. 



la. Mantle structure. 

 Fig. 2. Skeletonema costatum (Grev.) CI. Part of a chain. 



2a. Part of a more slender chain. 



2b. Sketch to show arrangement of connecting threads between cells. 

 Fig. 3. Thalassiosira decipicns (Grim.) Jorg. Part of a chain. 



3a. ^^alve view indicating arrangement of sculpturing. 

 Fig. 4. Thalassiosira rotula Mean. Part of a chain. 



Fig. 5. Plankloriiflla sol (Wall.) Schiitt. Valve view of ceil with old wing- 

 like expansion. 



5a. Valve view of cell developing new wing-like expansion. 



5b. Normal cell with arrangement of sculpturing on valve indicated. 



5c. Girdle view of a normal cell. 

 Fig. 6. Asteromphalus heptactis (Brcb.) Ralfs. Valve view with arrangement 

 of areoles indicated in one sector. 



