CYATHOPHYLLOIDEA. 



287 



rocks, may perhaps be referred, as previously remarked, to the Astrceidce ; 

 but many of the astrseiform corals usually placed in this genus, and 

 especially the so-called " Acervularias" of the Devonian rocks, are nearly 

 allied to Cyathophyllum. The corals in question agree in general struc- 

 ture, and particularly in the possession of an exterior vesicular zone, with 

 Cyathophyllum, but differ from this in the fact that the central tabulate 

 area is partitioned off and enclosed by a secondary and interior wall or 

 " mural investment." Another type which may be placed in this neigh- 

 bourhood is the Silurian g'enus ArachnopJiyllum ( = Stro?nbodes\ in which 

 the corallum is composite and astrseiform (figs. 163 and 164), but the 

 walls of the corallites, as also the septa, are very imperfectly developed, 

 while the visceral chamber is almost filled with vesicular tissue disposed 

 centrally in funnel-shaped layers. 



As the type of another group of the Cyathophyllidce, the great genus 

 Lithostrotion, so characteristic of the Carboniferous deposits of many 

 parts of the world, may be taken. The 

 corallum in this genus (fig. 165) is al- 

 ways composite, sometimes massive, 

 sometimes fasciculate, according as the 

 prismatic or cylindrical corallites are 

 or are not in direct contact with one 

 another. In internal structure, Lit ho - 

 strotion is built upon the type of 

 Cyathophyllum, each corallite having 

 an external vesicular zone and an inter- 

 nal tabulate area (fig. 166, b). The ve- 

 sicular zone is narrow, and the tabulate 

 area is wide, and is traversed centrally 

 by a well-developed styliform columella. 

 The septa are alternately long and 

 short, their disposition being clearly 

 tetrameral ; and the symmetry is dis- 

 tinctly bilateral, a well-marked fossula 

 being often recognisable. Thus, in the 

 species here figured (fig. 166, a), there 

 are fifty-six septa in all in each corallite, 

 twenty-eight of these being long ones 

 and a similar number being short. Of 

 the twenty-eight long septa, the four 

 leading septa are readily determined. 

 The "cardinal septum" (h) is shorter 

 than the others, and is placed in the 

 fossula, while the " counter septum " (g) is placed at the opposite end of 

 the compressed columella, a definite middle line to the corallite being 

 thus established. At right angles to the centre of this line are the two 

 " alar septa " (s s), and the remaining twenty-four long septa form four 

 groups of six septa each, corresponding with the four quadrants of the 

 corallite. Some of the species of Lithostrotion are not as regularly con- 

 structed as the above, but the same general type is preserved throughout 

 the genus. 



The genus Diphyphyllum, ranging from the Silurian to the Carbon- 

 iferous, appears to resemble Lithostrotion in general structure, but the 

 corallites of the fasciculate corallum are devoid of a columella. The 

 genus Eridobhylhtm, of the Silurian and Devonian rocks, again, seems 

 to differ from Diphyphyllum principally in the fact that the long, cylin- 



Fig. 165. — Fragment of a mass of Litho- 

 strotion Martini, of the natural size. 

 Carboniferous. (After De Koninck.) 



