MADREPORARIAN CORALS 75 



ridges, so that the surface is relatively smooth and striated 

 instead of being rough and ridged. 



Pachyseris. — The last of these genera that need be 

 mentioned here is Pachyseris, which shows the most extreme 

 form of modification of the original system of distinct 

 calices (Fig. 29). 



The coral is in the form of large rather thin cordate or 

 more irregular fronds attached by a short thick stem. The 

 under surface is a thin imperforate plate. The upper surface 

 consists of a series of concentric parallel ridges and valleys, 

 the valleys being traversed by an immense number of rela- 



FiG. 29. — Pachyseris. A part of a large frond showing the cahces completely 

 merged into parallel ridges and grooves, x 2 diams. 



tively thick and parallel septa. There is no indication 

 whatever of any distribution of these septa into discrete 

 calical areas. Pachyseris is a widely distributed but not 

 very common coral found in shallow water in the tropical 

 Indian and Pacific Oceans. 



Family 5. Eupsammiidae 



This family can readily be distinguished from the pre- 

 ceding families by the complete perforation of the walls 

 of the calices and, in most genera, of the septa as well. It 

 was formerly placed in the old division of Madreporaria 

 known as the Perforata, but in the general structure of both 



