SUB-GENUS PERONOPORA. 229 



vertical to the surface of attachment, but as the margins are 

 approached they become more recHned, and open by obhque 

 apertures on the surface. The ordinary coralHtes have the 

 same irregularly indented outline as is shown by the calices, 

 and are generally from i-i25th to i- 120th inch in diameter. 

 Interspersed with these are very numerous thick- walled circu- 

 lar tubules, the upper extremities of which appear on the sur- 

 face as the tubercles or spines previously alluded to ; while it 

 is by their inward projection into the visceral chambers of the 

 large corallites that the tooth-like indentations of the latter are 

 produced. The tabulae are mostly complete, concave, or hori- 

 zontal, and are fairly numerous ; while incomplete crescentic 

 tabulae (of the type of those of M. fj-ondosa, D'Orb., &:c.) ap- 

 pear to be commonly developed close to the mouths of the 

 calices. 



Obs. — Owing to the extreme tenuity and fragility of the 

 skeleton of this very peculiar form, it is exceptionally difficult 

 to prepare satisfactory sections showing its minute structure. 

 I have, however, succeeded in making both tangential and 

 vertical sections which enable a fair idea of its most important 

 structural features to be acquired, though there are still various 

 points which I have been unable to clear up, and it will be 

 needful to make further preparations before it will be possible 

 to entirely work out its characters. 



Tangential sections (PI. III. fig. ^b) are in many respects 

 very like similar sections of M. frondosa, D'Orb. The coral- 

 lites are irregularly oval or circular in shape, the irregularity 

 being due to the fact that the visceral chambers are encroached 

 upon by blunt tooth-like inward projections, due to the exist- 

 ence in the thick walls of numerous thick-walled circular tubuli 

 (" spiniform corallites"). These tubuli, as seen in section, 

 have dense dark borders surrounding a central clear spot, and 

 the blunt tubercles surroundinof the margins of the calices are 

 unquestionably their upper extremities. Many of the coral- 

 lites, though not all, show an excentrically perforated lamina, 

 partially extending across the visceral chamber, and appa- 



