450 II. L. Hawkins — Tuberculation of Holed ypoida. 



manner of its arrangement in Anorthopygus. Not only were the 

 sutures between the plates obscure in all the specimens available, bnt 

 there seemed no trace of a central median series passing vertically 



FlG. 2. Diagram showing the comparative arrangement of the tubercles (in 

 a half-interradius) in the Holectypoida. A, Pygaster semisulcatus ; 

 B, P. umbrella; C, Holectyjnis hemisplicericus ; D, H. depressus ; 

 E, Anorthopygtts orbicularis; F, Discoidea cylindrical G, Conulus 

 albogalerus. [The thick line represents the ambitus. The relative 

 proportions of the tubercles are not indicated.] 



