SUB-GENUS PERONOPORA. 227 



ones very variable in shape, but always of minute dimensions 

 and more or less angular form. The small corallites are 

 furnished with numerous complete and horizontal tabulse. 

 The larg^e corallites, thouofh sometimes furnished with sim- 

 ilarly horizontal and complete tabulae, are mostly provided 

 throughout part or the whole of their course with incomplete 

 curved tabulse, which form a series of vesicles on one side of 

 the tube, the remainder of the visceral chamber being occu- 

 pied by simple transverse partitions. 



Obs. — In the general aspect of its surface, this species is not 

 unlike the type-form oi M. ramosa, D'Orb., of which it might 

 be taken to be a variety. It is, however, distinguished from 

 this, apart from its encrusting habit, by the more pronounced 

 character and greater prominence of its monticules (PI. II. fig. 

 6), the smaller number of the interstitial tubes (PI. II. fig. ^a), 

 and its entirely different Internal structure. 



Tangential sections (PI. II. fig. 6<^) show that the corallum 

 is composed of two sets of corallites of different sizes and 

 entirely different structure. The large corallites are oval or 

 sub-polygonal in shape, with only moderately thickened walls, 

 each exhibiting in its centre, or on one side, a perforation due 

 to its possession of the same peculiar incomplete tabulae as 

 exist in M. frondosa, D'Orb., M. Ncwberryi, NIch., and M. 

 Selzvyiiii, NIch. All the Intervals between the large corallites 

 are filled In with the small angular or sub-anoular tubes. No 

 " spinlform corallites " appear to exist. 



Vertical sections (PI. II. fig. 6c) bring out, even more clearly, 

 the distinctions between the large and small corallites. The 

 large tubes are only slightly thickened as they approach the 

 surface, and some of them seem to possess only horizontal 

 tabulae, placed at moderate distances. Most of them, however, 

 possess tabulae of the same peculiar double type as is seen 

 in the species above alluded to. One side of the visceral 

 chamber, namely, is occupied by a series of strongly curved 

 tabulae, which have their convexities directed towards the 

 centre of the coralllte, and are so apposed as to give rise to 



