450 MT?. HERBERT L. HAWKINS ON 



Pygasteinna^. Apical system composed of five genital plntes, the 

 posterior one perforated or not. Madreporite central. Ocular 

 plates often very small. Radioles short, ac\iminate, longitudinally 

 striated. 



Lower Oolitic to Upper Cretaceoiis. 



Subfamily 1 . H o L e c t Y p i N ^• 



DiscoidiidfB with the periproct marginal or adoral in position. 

 Fifth genital plate smaller than the other four. Tuberculation 

 nsually sparse. Perignathic ridges low. No internal buttresses 

 to the test. 



Genus 1. HoLECTYPUS Desor. 



Holectypina:" with the characters of the subfamily. 

 Genotj^pe. H. depressus Leske. 



Subgenus 1. Holectypus sens. str. 



Holectypus with the posterior margin often elongated ; witli a 

 large periproct, marginal or adoral in position. Fifth genital 

 plate small and imperforate. Madreporite centiul and 

 prominent. 



Subgenotype. H. depressics Leske. 



Lower and Upper Oolitic. 



Subgenus 2. Ccexholectypus Pomel. 



Holectypus with a circular ambitus ; periproct of comparatively 

 small size, usually adoral in position. Fifth genital plate almost 

 as large as the others, and perforated. 



Subgenotype. C. macropygus Desor. 



Lower to Upper Cretaceous. 



Genus 2. Coptodlscus Cotteau &, Gauthier. 



Holectypinfe similar to CoenJiolectypus, but with deep excava- 

 tions along the plate sutures on the adapical surface. 

 Genotype. C, ncemice Cott. & Gauth. 



Genus 3. Lanieria Duncan. 



Holectypinfe similar to Ccenliolectypus, but globular in shape. 

 Genotype. L. lanieri d'Orbigny. 

 Upper Cretaceous. 



Subfamily 2. D i s c o i D 1 1 n .e. 



Discoidiidfe with a circular ambitus ; with the periproct on the 

 adoral surface. All five genital plates of approximately equal 

 size, the posterior plate perforated or not. Madreporite often 

 scattered over all five genitals. Perignathic ridges high. 

 Internal buttresses present on the adoral surface. 



