1 86 THE GENUS MONTICULIPORA. 



rounded tubes being situated at their angles of junction. Tab- 

 ulae fairly developed, complete and horizontal, increasing in 

 number as the mouths of the tubes are approached. 



Obs. — This very singular species was originally described 

 by Messrs Miller and Dyer {Joe. cit.) ; but I have, unfortunate- 

 ly, not been able to refer to the original paper. Its peculiar 

 helicoidal shape (PI. I. figs. 3, 3cr), and the fact of its being 

 built round a curved central tube which opens externally by 

 a round aperture, would alone distinguish the species, quite 

 apart from its internal characters. I do not know what view 

 was adopted by Messrs Miller and Dyer as to the origin of 

 this very unusual and apparently constant form, but I gather 

 from a letter from Mr Nickles, of Cincinnati, that after study- 

 ing the numerous specimens in his extensive collection, he is 

 disposed to regard its form as something peculiar to itself, and 

 not as due to the fact that it has grown round some foreign 

 organism. In such thin sections as I have made, it seems 

 certain that the central horn - like cavity is lined by a well- 

 defined calcareous layer (PI. I. fig. y), the structure of which 

 seems to be quite distinct from that of the corallites them- 

 selves ; and I was therefore at first disposed to regard the col- 

 ony as parasitic upon some such foreign object as a Tubicolar 

 Annelide, to which fact its peculiar forn^i might be ascribed. 

 Mr Nickles, however, is of the opinion that this calcareous 

 lining of the tube is really the epitheca of the colony ; and as 

 his opportunities of observation have been much greater than 

 mine, it is quite possible, and indeed probable, that he is 

 right in this opinion. Certainly, the fact that specimens no 

 bigger than the head of a moderate-sized pin should show the 

 same peculiar form and the same strange central tube as occur 

 in fully-grown examples, would militate very strongly against 

 the view that the spiral tube can be foreign to the corallum. 

 It reminds one of the "worm-like body" of Plciirodictyiini, 

 though it is not possible to assert that the two structures are 

 the same. 



In external characters the calices of M. calccola are thin- 



