4 8 4 



FOSSIL APOROSE CORALS. 



Ulophyllia, Favia, Heliastrcea, Rhymastrcea, and Stephanocoenia. 

 The Neocomian genera of Aporosa are Holocystis, Acanthocoenia, 

 Pentaccenia, and Bracltycyathus. Dasmia commences in the Neo- 

 comian, arid survives till the Lower Tertiary. The Cretaceous 

 rocks abound in Aporosa: among the genera are Onchotrochus, 

 Cydocyathus, Baryhelia, Diblasus, SynJielia, Diploctenium, Peplo- 

 utmlia, Pleurocora, Rhabdocora, Hexasmilia, Dactylosmilia, Hymen- 

 ophyllia, Glyphophyllia, Eugyra, Meandrastrcea, Stelloria, Aspidiscus, 

 Stenosmilia, Phyllastrcea, Placophoria, Stylastrcea, Psammophora, 

 Heteroccenia, Elasmocoenia, Haldonia, Placastrcea, and Dictyophyllia. 

 Cretaceous genera -which survive to the Lower Tertiary period are 

 Smilotrochus, Stylocyathiis, Placosmilia, Dendrosmilia, Stylocora, 

 Barysmilia, Columnastrcea, PJiyllocoenia, and Holoccenia. While 

 among genera which first appear in the Cretaceous rocks and still 

 survive are Caryophyllia, Lophosmilia, Diploria, Leptoria, Myceto- 

 pliyllia, Phrogyra, and Hydnophora. 



Several genera of corals are peculiar to the Lower Tertiary, such 

 as Ceratophyllia, Circophyllia, Pattalophyllia, Stylangia, Desmodadia, 

 Cyathromorplia, Areacis, Anisocoenia, Narcissastrcea, Aploccenia, 

 Heterogyra. But many genera which still survive date from the 

 Lower Tertiary period. Among these are Flabellum, Sphenotrochut, 

 Placocyathus, Platycyathus, Leptocyathus, Paracyatlms, Ceratotrochus, 

 Amphelia, Oculina, Stylophwa, Asterosmilia, Asterangia, Solenastrcea, 

 and Plesiastrcea. The Middle Tertiary genera comprise Astrohelia, 

 J/aplohelia, Lithopliyllia, Bathangia, Cladangia, Teleiophyllia, Mon- 

 ticulastrcea,Favoidea, D'Archiardia, Antillastrcea, and Diplothecastrcea. 



Genera which commence in the Middle Tertiary, and still survive, 

 include Conocyathus, Deltocyathus, CoBnocyatlius, Lopliolielia, Diclw- 

 coenia, Echinopora, and Desmopliyllum. In the Upper Tertiary 

 Eusmilia is found. 



Asteroidea. The true star-fishes are characterised by having the 

 digestive and ovarian organs contained within the arms. An attempt 

 has been made to classify star-fishes by the arrangement of the am- 

 bulacra! organs into those with four rows, those with two rows, and 

 those in which ambulacral plates separate the pores ; but none of these 

 groups are natural, and the only scientific division of star-fishes fur- 

 nishes no palseontological characters. 



Fig. 92. Palceaster. 



The oldest fossil star-fishes are found in the Cambrian rocks, Palce- 

 aster, Urasterella, and Palceasterina being common to the Cambrian 



