ZAPHRENTOIDEA. 



295 



corallum is simple, conical, turbinate, or cylindrical in form, more or less 

 curved, and showing a conspicuous fossula in the obliquely placed calice. 

 The fossula in different species is on the convex side of the corallum 

 (" dorsal "), or on the concave side (" ventral "), or in rare cases is lat- 

 eral. The septum included therein is usually very short (fig. 172, A and 

 b), and may be obsolete, while more or fewer of the septa on each side 

 generally bend round, and, partly coalescing, enclose the wide inner 

 end of the fossular groove. The septa are moderately numerous, al- 

 ternately long and short, the latter being commonly rudimentary and 

 sometimes partly obsolete. The long septa extend a considerable dis- 

 tance inwards towards the centre of the visceral chamber, and often 

 show a; tendency to coalesce in groups. Dissepiments are sparingly 

 developed in the outer zone of the corallum, but tabulae are largely 

 developed, and pass from side to side of the visceral chamber (fig. 

 172, d), often becoming united to form large arched vesicles. The 

 species of Zaphrentis are mainly Carboniferous and Devonian, but 

 some forms referred to the genus are Silurian. 



The Devonian and Carboniferous genus Amplexus is closely similar 

 to Zaphrentis, but the simple corallum is usually cylindrical in form, 

 while the septa are much less perfectly developed, being confined to the 

 margin of the visceral chamber, and thus leaving exposed a large central 

 space occupied by nearly horizontal, complete tabulae. 



In the Carboniferous genus Lophophyllum there is a simple conical 

 corallum of small size (fig. 174), which agrees with Zaphrentis in the 

 scanty development of dissepiments and the possession of complete 

 arched tabulae. There is also a small fossula, which lodges the " cardinal 

 septum" (fig. 174, B, h), this being shorter than the other septa. On the 



Fig. 174. — Structure of Lophophyllum eruca, from the Carboniferous Limestone, Scotland. 

 A, Side-view of the corallum, enlarged slightly ; b, Transverse section of the same, enlarged four 

 times ; c, Longitudinal section of the same, similarly enlarged, h, Cardinal septum ; g, Counter 

 septum ; /, Tabulse. (Original.) 



other hand, the " counter septum " (fig. 172, B, g) is greatly developed, 

 being much longer than the other septa, and having its inner extremity 

 swollen. This enlarged septum has been regarded as a true columella, 

 but an examination of very young specimens shows that its real nature is 

 as just described. The remaining septa are unequal in size, but a division 

 into alternately long and short septa cannot be recognised. 



In the Carboniferous genus Menophyllum, again, there are three 

 fossulae, the largest being on the dorsal side of the corallum, and lodging 

 the "cardinal septum," while the other two are lateral and lodge the 



