92 Dr. II. A. Nicholson on the 



able to C.fro)idosus, D'Orbigny, or whether two superficially 

 similar forms have not been included under this name. Sections 

 of my specimens taken parallel with the surface (PI. V. fig. 11) 

 show very striking features. The majority of the corallites 

 are oval or rounded, and have very thick walls. In the spaces 

 between the ordinary corallites are placed smaller oval or 

 rhomboidal tubes, of the same character as the preceding ; 

 and, lastly, there is a great number of very minute, circular, 

 interstitial tubuli, the Avails of which are so dense as to look 

 black in sections. These smallest tubuli are irregularly 

 scattered amongst the larger ones, and very often are so placed 

 as to project into the cavity of one of the large corallites. 

 In long sections (PI. V. fig. 9 a), the corallum is seen to con- 

 sist of two strata of corallites, which are directed outwards at 

 right angles and in opposite directions from a thin undulating 

 median lamina, with which they are connected by delicate 

 curved tabula;. Three kinds of corallites are present, as in 

 C. jyefropolitanus. In one kind, the largest of all, the interior 

 of the tube is divided into two halves by a delicate wavy 

 vertical septum ; in one half of the tube the tabulae are 

 more or less curved, and in the other half they are generally 

 straight and less numerous. In another kind, rather smaller 

 than the preceding, the tubes are simply crossed by straight, 

 comparatively remote tabulje. Lastly, there are numerous 

 minute tubuli, in which the tabulse are very closely set. 



Constellaria antheJoidea, Hall. 

 Constellaria antheloidea, Nich. o^>. cit. p. 214. 



In its internal structure this genus very closely approaches 

 Chcntetes [Monticulijjora) ; and it is doubtful if the marked ex- 

 ternal peculiarities which it presents are sntficient to justify 

 generic distinction. Vertical sections, taken through the 

 centre (PI. V. fig. 10 a), show that the corallites are neaidy 

 vertical in the middle of the corallum, and are divided by 

 regular but very remote tabulse. In approaching the surface 

 the corallites bend outwards, and divide by fission into a num- 

 ber of more slender tubes, w^hich are generally traversed by 

 very numerous and close- set tabulae. In cross sections (PI. V. 

 fig. 10) the corallites are seen on the circumference of the 

 section to be cut longitudinally, as they bend outwards, and 

 they are here finely tabulate, whilst a few of the larger tubes 

 appear to be destitute of tabulse. In the centre of the section 

 the corallites are divided transversely, and they are here thin- 

 walled and polygonal. The calcite filling the tubes is divided 



