16 PEOF. P. MAETIN DUKCAN's EEVISION OP THE 



III. Alliance PLACOTROCHOIDA. 



Simple Turbinolidse, free or attached, compressed, with an essential, 

 more or less lamellar or elongate columella, rarely with pali. 

 Genus Placotrochus, Ed. & H. 

 Genus Sphenotrochus, Ed. & H. 

 Genus Nototrochus, Duncan. 

 Genus Placocyathus, Ed. & H. 

 Genus Platytrochus, Ed. & H. 



Genus Placotrochus, MM. Milne-Edwards Sf Jules Haime, 



Ann. des Sci. Nat. 3® ser. t. ix. p. 282 (1848), amended. 



The corallum is simple, straight, cuneiform, flabelliform, and 

 compressed or cornute, or more or less cylindrical and compressed. 

 The columella is essential and is lamellar, horizontal, sharp, and 

 entire at the surface, or crenulated. Septa exsert or not. Costse 

 developed, and often in crests or spinulose. 



Localities. — Becent. Chinese seas, Philippines, N. Australia. — 

 Fossil. Miocene of "West Indies, Australia, Europe. 



This is a well-marked genus, and some of the species are much 

 compressed and extended laterally ; others are deltoid and com- 

 pressed ; and one Sicilian form is cornute, with an epitheca. 

 The lamellar and essential columella is very characteristic. 



Genus Sphenoteochus, MM. Milne-Edwards Sf Jules Raime, 

 Hist. Nat. des Corall. vol. ii. p. 65. 



The corallum is free, straight, cuneiform, compressed. Septa 

 exsert or not ; the principal reach the essential lamellar columella, 

 which is lobed or knobbed at the free surface on the floor of the 

 elliptical calico. Base bluntly pointed, truncate, or emarginate. 

 Costse projecting straight or more or less in zig-zag. Lateral 

 costse crested or not. 



Localities. — Becent. Mediterranean and N. Africa ; coast of 

 Brazil ; European coasts of N. Atlantic ; S. Australian coasts. — 

 Fossil. Cretaceous : Germany, Eocene of Prance, Belgium, and 

 Alabama. Miocene of France and Germany. Pliocene of 

 England. Cainozoic : Australia and New Zealand. 



The species described by M. de Promentel from the Cretaceous 

 of France would appear to be more like a BlacotrocJius than a 

 Sphenotroclius . 



There is a common little simple coral in the Tertiaries of Aus- 

 tralia which has given the Eev. T. "Woods and myself much 



