Species o/" Luffaria from Yucatan. 225 



sarcode or horny material has penetrated amongst the granules 

 instead of forming a decided wall around them, and thus the 

 fibre is not tubular, as in most of the Luffarida, but solid ; 

 and this feature is characteristic. The diameter of the granular 

 core is uniformly (excepting, of course, at the joints or angles 

 of the meshes) about 1-1 600th of an inch, and the thickness 

 of the horny material around it is in the young growth also 

 about 1-1 600th of an inch, thus making the diameter of 

 the young fibre 3-1600ths of an inch; while that of the 

 oldest fibre measures about 16-1600ths or l-100th of an inch. 

 The horny skeleton-network does not present any radial lines, 

 but is a reticulation of meshes of nearly uniform figure and 

 character, and is apparently increased by the addition of one 

 polyhedral mesh after another, through the extension of new 

 fibre chiefly projected from the angles of the already formed 

 meshes, which branchlets soon bifurcate, extend, and unite 

 to form new meshes. The round-edged ridges on the outside 

 of the tube are simply extended growths of the ordinary net- 

 work, which is produced more in one place than another ; 

 and they seem to occur much like a succession of rings, though 

 the circle is seldom complete, and often an appearance is as- 

 sumed similar to that of the surface of the Meandrina coral. 

 The rim of the aperture consists of fine, young, reticulated fibre 

 imbedded in very dark-coloured sarcode (nearly black, indeed) ; 

 and the extension of the tube both in length and thickness ap- 

 pears to be produced by the addition of similar ring-like struc- 

 ture growing apically, endogenously and exogenously. The 

 dermal reticulation supports a strong glazed cuticle of a dark 

 brown colour, through which may now be seen protruding the 

 plain and bifurcated ends of the young fibre. This dermal 

 covering is pierced at irregular intervals with pores, which 

 measure from l-50th to l-25th of an inch in diameter, consider- 

 able spaces occurring in it in which no pores can be detected ; 

 but although the pores are thus found scattered and isolated over 

 some parts of the surface, they are elsewhere found in groups 

 of several together both in the furrows and on the ridges. 

 They lead directly into the " subdermal cavities," which are 

 large and roomy, and which, besides communicating with the 

 areolar structure behind them by means of the usual sphinctral- 

 openings in their sarcodic walls, sometimes communicate with 

 each other in a similar way, thus accounting for the paucity 

 of pores in some parts of the dermal layer. The areolar 

 structure of the interior is a series of roomy chambers, which 

 extend from the subdermal cavities across the walls of the tube, 

 and which communicate with each other by means of circular 

 openings in the sarcode which tympanites the interstices 



