chief Generic Types of Pal<jeozoic Corals. (U 



or less extensive zone of vesicular tissue, composed of nume- 

 rous rows of minute cells. Septa with their sides and edges 

 smooth, always symmetrically developed and regularly ar- 

 ranged. No true columella is present ; but the septa usually 

 extend to the centre of the visceral chamber, wliere they par- 

 tially coalesce or are twisted together, so as to form a small 

 spurious columella projecting into the bottom of the calice. 



The form of the corallum differs very much in different 

 species of Cyatliophyllum. In the simple forms the corallum 

 is more or less of a conical or cylindro-conical figure, usually 

 more or less bent or curved towards the base, and often with 

 well-marked accretion-ridges. Good examples of these are to 

 be found in G. mygustum^ Lonsd., G. Mio'chtsoni, E. & H., 

 C. Stutchburyij E. & H., G. Roemeri, E. & H., G. ceratites^ 

 Goldf., and G. obtoi-tum, E. & H. The compound forms of 

 Cyathoj)hjUum assume very different aspects according to their 

 mode of growth. Some, such as G. articulation^ Wahl., and 

 G. ccespitosum^ Goldf., form fasciculate masses, in which the 

 corallites are long and cylindrical, and remain distinct from 

 one another. Others, such as G. truncatum, Liim., and 

 C. paracida, M'Coy (PL VII. fig. 7), exhibit the purest form 

 of compound calicular gemmation, and form inverted pyra- 

 midal masses, the bases of which are formed by the parent 

 corallite. Others, again, such as G. Itexagonum^ Goldf., G. holo- 

 m'ensej Blainv., G. Sedgwickit, E. & H., and G. reyium, PhilL 

 (PI. VII. fig. 9), constitute astraiiform masses, in which the 

 coi'allites are generally firmly united laterally, and assume a 

 polygonal form from mutual pressure. Finally, one species at 

 any rate, viz. G. helianthoides^ Goldf., appears to have been 

 sometimes simple and sometimes compound. In the compound 

 Gyatliophylla calicine gemmation is the predominant mode of 

 increase, though lateral gemmation obtains in some. 



As regards their internal structure, the corals which are 

 referable to the genus Gyathophyllum appear to be marked out 

 with sufficient distinctness. The epitheca is generally thin, 

 but well developed, and marked with fine concentric stria3 ami 

 more or less consj)icuous annulations of growth. Very often 

 there are vertical lines or ridges corresponding with the se{)ta 

 within ; and these are very conspicuous in some forms, as, for 

 example, in G. anyustum, Lonsd., and G. hisectum, Lindstrom. 



The tabula? never extend completely across the visceral 

 chamber, as they do in Zaphrentis and Amplexus^ but are 

 always confined to a zone or area occupying the centre of tiie 

 coral. This tabulate area is sometimes very extensive, at 

 other times more or less contracted ; and within it the tabuho 

 are usually very closely set, often bifurcating and coalescing 

 with their neighbours (PI. VI. jig. 1, ^: Pi. Vll. figs. 7 A, 9 a). 



