TRIBE I. ASTR^ACEA. 285 



a proper medial trench; surface consisting of short denticulate lamella less than half an 

 inch long, imperfectly or not at all radiate. 



6. ZOOPILUS. Polyps all scattered. Corallum without a medial trench, surface con- 

 sisting of long lamellae, with thinner lamella intermediate; only the latter interrupted 

 by oririmes and short, the polyp-mouths being situated in the intervals between the large 

 lamellte. 



III. Bud/ling; attached. , 



7. PAVONIA. Foliaceous, unifacial or bifacial, sometimes glomerate or subramose; 

 polyps not in distinct series, or imperfectly so. Coralla compact, surface plane or without 

 parallel ridges; no excavate cells, lamella; distinct, and nearly or quite entire. 



8. AGARICIA. Foliaceous, unifacial or bifacial ; polyps in more or less perfectly 

 transverse series. Coralla with transverse ridges and fossa?, sometimes consisting of 

 coalescent excavate cells, and irregular; lamellae alternately smaller, nearly or quite 

 entire. 



9. PSAMMOCORA. Bifacial and fbliaceous, or glomerate and columnar. Coralla with 

 or without large excavate cells ; lamellte equal, and very minutely ragged-denticulate and 

 grnnulous, indistinct. 



The following table exhibits the relations of the genera here 

 adopted, to those used by the authors whose names are placed above 

 the several columns. 



72 



