ROBERTS— UPPER SILURIAN CORALS, 



59 



division of Silurian Zoantliaria, differing widely from the cnp- and 

 star-corals, both in shape and character. They are all composite — no 

 single tube or cup could be a millepore, either in fact or by com-tesy, 

 for the name implies the aggregation of a number of polyps having 

 more direct connection with each other than the cup-corals. In 

 shape they are both massive and branching. The first two genera, 

 Heliolites and Favosites, are distinguished from each other by the ab- 

 sence of those septa in the latter that form such elegant star-like 

 discs as they fill up the calicos of the former. 



Heliolites, i.e., sun-coral, is so named from the sun-like appearance 

 of its calicos. H. interstinda has these cahces^closely set, and equal in 

 distance from each other, the intervening space, called the coenenchj- 

 ma, bemg filled with polygonal cells. Upon the surface of H. Mur- 

 cliisoni the caHces are not closely set, and vary in approximation. S. 

 megastoma is easily known from either ; large, closely set, calices cover 

 its surface, and what coenenchyma their nearness permits is made up 

 of square cells. All these are massive corals irregularly hemispheri- 

 cal in form, and having a basal-plate strongly marked with concentric 

 ridges. The branching Hehohtes are still more elegant. H. Gh-ayii 

 is rudely branched, and bears its sun-like calices on both surfaces. 

 The only known specimen of this species was found in the Wenlock 

 shale of Walsall, and is in the cabinet of its discoverer, Mr. Gray, of 

 Hagley. S". inorclinata is decidedly arborescent in form, very 

 slenderly branched, and bearing cahces, whose rarity is made out by 

 the extreme beauty of their form. This, however, is peculiar to 

 Lower Silurian rocks, and I only introduce it here to complete my 

 sketch of Heholitic corals. 



The genera Flasmopora and Fro]^ora differ from HeHolites, mainly 

 in the appearance of their surfaces, the septal rays being prolonged 

 beyond the edge of the caHce, and united to other rays which cover 

 the coenenchyma. In every species of these three genera the number 

 of septa contained in each cahce is twelve. 



Next come the Favosites. These have no intervening coenenchyma, 

 the coral being simply a bundle of tubes. The radiating septa of 

 their calices are only developed in one species, and that a rare one, 

 F. Hismgeri. F. Gothlanclica is the typical form ; this has strongly 

 walled tubes, which, coming up to the surface, cover it with a cali- 



