R. F. Tomes — Palceozoic Madreporaria. 



99 



I place this peculiar form in the vicinity of Cyathaxonia, though 

 only on account of the open loculi, and am somewhat doubtful as to 

 its real affinities. There is no true wall, and when the epitheca 

 is worn off, the edges of the porous septa are exposed. But the 

 absence of a wall is compensated for by the ring of endotheca which 

 takes its place and binds the septa together outwardly. 



As it is quite possible that the species on which I here propose to 

 form a new genus is no other than the one described by M'Coy 

 under the name of Cyathaxonia Siluriensis,^ I adopt for it the specific 

 name given by him. 



Hemiphylltjm Silukiensis, M'Coy, sp. ? 



Cyathaxonia Sihiriensis, M'Coy ? 



The corallum is small and cornute, the curvature being sometimes 

 confined to the small extremity, but is more frequently uniform 

 throughout its whole length. 



The epitheca is thin, somewhat annulated, and it does not ever 

 extend to the margin of the calice. When well developed, it has a 

 well-defined upper margin, above which the calice projects ; but 

 when it is less complete, the upper margin is ill defined, and it does 

 not always extend more than half-way up the corallum. 



m 



Ymw 



Fig. 2. 



.*/ 



Fig. 1. 



Hemiphyllum Siluriensis, M'Coy,sp.? 

 Magnified 2+ times. 



The calice is circular, shallow, and saucer-shaped, and when un- 

 worn the columella is nearly hidden by the septa which run into it. 

 The outer ends of the septa project upwards, in the position usually 

 occupied by the wall, and, with the abundant endotheca, form the 

 margin of the calice. They are twenty-six in number, irregular in 

 development, nearly equal in size throughout, and there is no 

 distinction between the cycles. All of them pass inwards to the 

 columella, the irregular papillee of which blend with those of the 

 septa, and the exact union of the columella and septa is obscured. 

 The whole of the septa are perforate, but the perforations have no 

 definite arrangement, and each septum divides into two near the 



1 Ann. and Mag. Nat. Hist. 2nd series, vol. vi. p. 281, 1850. 



