CCELENTERATA. 169 



Family Syringoporid^e. — Cannapora, Syringopora, Thecostegites. 

 Family Tetradiid.e. — Tetradium. 

 Family Thecidje. — Thecia. 



Subclass Alcyonaria. 



Family Bolboporitld.e. — Bolboporites. 



Family HELiopoRiDiE. — Heliolites, Lyellia, Plasmopora. 



Family Monticuliporid^:. — Dekayella, Dekayia, Diplotrypa, Monotrypa, 



Monotrypella, Monticulipora, Nebulipora, Nyctopora, Prasopora. 

 Family Stelliporid^. — Stellipora. 



CLASS HYDROZOA. 



This class is represented in palaeozoic rocks by carbonaceous horny skeletons, 

 called Graptolites. They are usually flattened, forming a thin film between shaly or 

 slaty layers, and generally, in whatever rocks they occur, they are more or less com- 

 pressed. Specimens are found in clay nodules and in calcareous clay beds, at Cin- 

 cinnati and vicinity, which are cylindrical branching bodies, or have subquadrate stipes, 

 covered with a thin, carbonaceous coating. The interior of one species is divided 

 by longitudinal partitions of thin, carbonaceous films, into three departments, one 

 of which is only about half the capacity of either of the other two. The denticulated 

 edges on flattened films become projecting cells on more perfect specimens. The 

 projecting cells may be subcircular or angular, and lead directly to the interior. 

 When the interior substance is absent, and the cells are pressed together, instead 

 of being pressed into the stipe, there is presented a diagrammatic side view of the 

 cells, which furnishes the usual saw or denticulated aspect, but which gives a very 

 imperfect, and frequently a very erroneous, idea of the form of the animal. This 

 was the first Order of organisms to reach a high state of development, and the 

 first to become extinct. 



ORDER GRAPTOLIDA. 



Family Callograptid^e. — Acanthograptus, Callograptus, Cyclograptus, 



Dendrograptus. 

 Family Dictyonemid^e. — Calyptograptus, Dictyonema, Rhizograptus. 

 Family Graptolitidje. — Cladograptus, Climacograptus, Clonograptus, Di- 



cranograptus, Didyraograptus, Diplograptus, Graptolithus. 

 Family Glossograptid^:. — Glossograptus, Retiograptus. 

 Family Nem agraptid^e. — Nemagraptus. 

 Family Monograptid^e. — Monograptus. 

 Family Inocaulid^e. — Inocaulus. 

 Family Meg alogr aptid^e. — Megalograptus. 

 Family Oldhamihle. — Oldhamia. 

 Family Phyllograptid.e. — Phyllograptus. 

 Family Ptilograptid^e. — Ptilograptus. 

 Family Rastritid^e. — Rastrites. 

 Family Retiolitid^e. — Retiolites. 



