§ 19. SILURIAN ZOOPHYTES AND MOLLUSCA. 785 



that a reference to works expressly devoted to the subject 

 can alone convey an accurate idea of this first, and most 

 ancient, fauna of our planet, of which any vestiges have 

 hitherto been obtained.* 



Of the corals, the Catenipora or chain-coral (ante, p. 644), 

 Cyathophyllum (p. 641), Astrcsa, and many large species 

 of Porites, Strombodes, &c. are among the prevalent 

 forms : and are often aggregated and cemented together 

 into large masses of limestone, on the surface of which the 

 stars or cells of the corals appear in relief. The slabs 

 of Dudley limestone, embossed with these fossils, must be 

 familiar to every intelligent observer. 



The Graptolttes, which are extinct zoophytes allied to the 

 Pennatulce,\ and Tentaculites, appear throughout these 

 deposits, especially in the lowermost. They occur in the 

 equivalent strata of Sweden, Norway, Russia, and North 

 America. 



The Crinoidea consist of several genera, as Cyathocrinus, 

 Actinocrinus, Hypanihocrinus,\ &c. which also abound in 

 the upper palaeozoic deposits ; and some that are peculiar, 

 as Echinosphcerites, and the family of Cystidece (ante, 

 p. 656), that includes several genera, which, according to the 

 observations of M. Von Buch, are only known in the Silurian 

 system. 



Mollusca. Of the simple bivalves, species of Area, 

 Cardiola, Cardium, Modiola, Mytilus, Nucula and Avi- 

 cula, are met with ; proving that these genera, which now 



* The beautiful and accurate plates by Mr. Scharf, in Sir E. Mur- 

 chison's Silurian System, contain representations of a large proportion 

 of the British species. Many are figured in the Geol. Transactions, and 

 in the Palaeontological Journal, and in Sowerby's Mineral Conchology : 

 and in Professor Phillips' Figures and Descriptions of the Palaeozoic 

 Fossils of Cornwall, Devon, and West Somerset. 



f Medals of Creation, p. 290. 



J A beautiful new species of this genus from the Wenlock limestone 

 of Walsall, is figured in the London Geological Journal, pi. 21. 



