298 ZOANTHARIA. 



lateral, the cardinal and alar septa being clearly recognisable, in well-pre- 

 served specimens, by the pinnate arrangement of the costal furrows on 

 the exterior of the corallum (fig. 156). The cardinal septum is reduced 

 in size, and usually occupies the centre of a large fossula (fig. 178, a), but 

 in some species {e.g., in S. europium) a fossula is wanting. The lower 

 part of the visceral chamber is more or less extensively filled up with 

 stereoplasma, and the upper part of the same is crossed by irregular 

 tabulae, dissepiments being also developed in moderate numbers. The 

 centre of the visceral chamber is occupied by a large, irregularly reticu- 

 lated or trabecular pseudocolumella (fig. 178, a), with which the inner 

 ends of the long septa are directly connected, and which is highly 

 characteristic of the genus. The species of Streptelasma are mainly 

 Ordovician, but Silurian forms have also been recorded. The genus 

 Ptychophyllum (if judged by the structure of the mushroom - shaped 

 P. patellatum of the Silurian rocks) is very closely related to Strep- 

 telas?na, the principal difference being that in this case the pseudo- 

 columella is produced by a twisting together of the 

 thickened inner ends of the longer septa. If, as 

 maintained by Lindstrom, these two genera are to 

 be regarded as identical, the name of Ptychophyl- 

 lum will have to be suppressed in favour of the 

 older title of Streptelasma. 



Lastly, we may possibly place among the Zaph- 

 rentoidea the small, simple Palaeozoic corals 

 which constitute the genus Lindstrcemia (fig. 179). 

 These forms agree with the typical Rugosa in 

 the pinnate arrangement of the septa and the 

 resulting bilateral symmetry of the corallum, but 

 they do not appear to possess a fossula. The 

 Fig. 179. — Lindstroc- distinctive feature in the genus is the fusion of 



mia Dalmani A por- th t b the j r • d t f t f 



tion of top of the theca tin i • i • r r • ^ 



is broken, in order to pseudocolumella, which is often of great size and 

 show the interior of the projects into the floor of the calice. The lower 

 portion of the visceral chamber is more or less 

 extensively filled up by stereoplasma, but dissepi- 

 ments and tabulae are scantily developed in its upper portion. The 

 species of Lindstrcemia are mostly Ordovician and Silurian, but the 

 genus survives into the Carboniferous period. 



III. Cystiphylloidea. 



The section of the Cystiphylloidea comprises those Rugose Corals 

 in which endothecal tissue in the form of dissepiments is in general 

 extensively developed, while tabulae are absent or are incompletely 

 developed, and the septa are more or less imperfect, and may be 

 reduced to mere marginal striae. When the septa are so far de- 

 veloped as to enable this point to be determined, it can be shown 

 that the symmetry of the corallum is distinctly bilateral, and in some 

 cases a well-marked fossula is present. The Cystiphylloid corals are 

 wholly Palaeozoic, and are confined to the Silurian and Devonian 

 rocks. 



Family 1. Cystiphyllidce. — This is the typical family of the Cysti- 



