MADREPORARIA PERFORATA. 319 



On the other hand, a distinct transition between Favosites and Syrin- 

 gopora is effected by the Silurian genus Syringolites, in which the coral- 

 lum (fig. 202) is quite similar in general structure to Favosites, being 

 composed of thin-walled polygonal corallites, the faces of which are per- 

 forated by longitudinal rows of distant mural pores, but the tabulae are 

 curved, and are depressed centrally so as to produce by their invagination 

 a vertical median tube running down the middle of each visceral chamber. 

 The Devonian genus Roerneria, again, seems to offer a similar transition 

 between Pachypora and Syringopora. In this remarkable type, the 

 corallum is closely similar in general structure to that of Pachypora, 

 being composed of contiguous polygonal corallites, with distinct walls 

 which are greatly thickened internally by a secondary deposit of stereo- 

 plasma, and are perforated by well-marked tubular mural pores, but 

 the tabulae are funnel-shaped and are invaginated in a manner precisely 

 similar to that which is so characteristic of Syringopora. 



The genus Romingeria, of the Silurian and Devonian rocks of 

 North America, affords another transitional link between the Favo- 

 sitidce and the Syringoporidce. The corallum in this genus (fig. 203) 

 is lax and spreading, erect or semi-erect, and 

 composed of cylindrical tubular corallites which 

 are produced by gemmation in umbellate whorls 

 or verticils. The tubes are largely free, but 

 where their walls come in contact, the visceral 

 chambers are placed in communication by dis- 

 tinct mural pores. The tabulae are remote, and 

 in general horizontal, and the septa are repre- 

 sented by vertical rows of calcareous spines. «^$ 



Family 5. Syringoporidce.— -This family includes Fig 203 ._ PortIon of 

 a number of Palaeozoic corals in which the skele- the corallum of Romin- 



t, r , • r / r gcria umbcllifera. of the 



tOn IS COllipOSlte, USUally faSClCUlate in form (figs, natural size. Devonian 



204-207), and is composed of cylindrical coral- gS^^orijSST'^ 

 lites which in general are not in actual contact, 

 but mostly have their visceral chambers placed in direct communica- 

 tion by means of hollow, cylindrical connecting-processes or horizontal 

 platforms, which are periodically produced. In many cases the coral- 

 lites come into actual contact in parts of the corallum, and where 

 this occurs their walls are pierced by mural pores similar to those 

 of the Favositidce. The tabulae are well developed, and are usually 

 funnel-shaped, but they are sometimes vesicular, or may, rarely, be 

 simply curved. The septa are in the form of vertical rows of cal- 

 careous spines. The mode of increase is by basal or stolonal gem- 

 mation, or by the production of new buds from the connecting- 

 processes or floors. The oldest members of this family appear in 

 the Ordovician rocks, and the last appear in the Carboniferous. 



The affinities of the Syringoporidee have been much disputed, and 

 the type-genus Syringopora has commonly been placed among the 

 Alcyonaria, and has been regarded as a near ally of the recent 



