PLATE II. 



UiNTACRiNUS sociALis Grinnell (page 21). 



Fig. la. Diagram showing the structural arrangement of the plates in the test, 

 lb. Specimen showing hasals and portions of radial and interradial areas. 

 Ic. Lateral vie w^ of arm with attached pinnules. 

 Id. Zizygial surface of hrachial plate, 

 le. Articular surface of brachial plate. 

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