ANTHOZOA 21 



(Diplograpsus, fig. 3, 5, ami Didymograpsus, fig. 3, 4) are Cam- 

 brian forms. Rastrites (fig. 3, 6) had the polypes only in one 

 side, and they are less crowded: it characterises Barrande's divi- 

 sion E of the Lower Silurian beds of Bohemia, and has not yet 

 been found in Britain. The Graptolites occur in argillaceous 

 strata, especially in the mud-stones of Wales and Cumberland, 

 and in the alum-slates of Sweden. These beds remind one of 

 the mud bottoms in which the Virgularia and other long and 

 slender graptolite forms of " Pennatulidse" flourish in forest- 

 like crowds. The primeval Graptolite may have presented a 

 more generalized polype structure than is now met with in 

 the specially differentiated Sertularians and sea-pens. 



Class II.— ANTHOZOA. 



In this class of Polypes the tentacles are hollow, and, in 

 most, with pectinated margins. The polypary is usually in- 

 ternal, and forms the bodies more properly called "corals 

 and " madrepores." 



Asteroida. — Great doubt attaches to some of the fossils 

 referred to this class of Polypi. The terms " Gorgonia" and 

 " Alcyonium" have been applied to objects not well under- 

 stood, and usually proving to be Bryozoa and sponges. The 

 Lower Silurian fossil called Pyritoncma consists of a fasciculus 

 of silicious fibres, and has been supposed to be related to the 

 glass zoophyte (Hyalonema). The miocene deposits of Pied- 

 mont contain a species of the Mediterranean genus Corallium, 

 an Antipathes, and an Ids (or Isisina, d'Orb.), winch is also 

 found in Malta. The London clay contains one coral {GrapJm- 

 laria), referred to the Pennatididce, and two Gorgonidce [Mop- 

 sea and Webster ia). 



Actinoida. — The lamelliferous or stony corals are (next 

 to the Testacea) the largest and most important class of 

 invertebrate fossils. They attained a great development in 



