Madreporarian Suhfnmihf Montiporinae. 125 



are confined to the upper surface. In the case of the branched 

 specimens the tips of the branches whicli correspond with 

 tlie growinf^ edge of the explanate forms consist entirely of 

 tlie streaming hiyer, and this may be seen forming the axis 

 of all the stems. Tlie cortical hiyer, which gradually thickens 

 the branches, can in most cases be seen to be formed of 

 threads bending outwards at right angles to the direction of 

 the axial streaming layer. 



Leaving, then, the jirimitive basal streaming layer, we 

 have to consider the variations presented by the upper thick- 

 ening layer just described : — 



(1) It may merely thicken the streaming layer gradually 

 as a filamentous reticulum, the surface in which the calicles 

 open remaining all the time smooth. In reference to the 

 level surface, 1 have called this group " glabrous," and under 

 it I have arranged some thirty different types (fig. 3 a). 



(2) The thickening reticulum may grow faster than the 

 calicles, causing the interstices to swell up into ramparts 

 surrounding pits, in the bases of which the calicles open. I 

 have called this the " foveolate " group, after the most 

 extreme type, M. fovaolata of Dana. 



Between these two come specimens which are foveolate 

 while in rapid growth, but eventually become smooth ; these 

 I have called " glabro-foveolate." I have found some twelve 

 foveolate types and five glabro-foveolate. 



One specialization of these ramparts has a curious resem- 

 blance to true protuberant calicles. This appears to have 

 misled Dana in his ascription of true calicles to M. caliculata. 



(3) The thickening reticulum shoots up into papillae which 

 rise up above the general surface. There are several more or 

 less distinct variations of the " papillate " specialization, 

 which at the moment of writing is shown by at least tiiirty- 

 three types (fig, 3i). 



The leading differences are as follows : — (a) reticular 

 uprisings froth up the interstices over irregular patches of 

 different sizes ; {h) the papilla3 are always in some relation to 

 calicles, forming hoods or mounds, on the outer faces of 

 which calicles open ; (c) the papilla3 run together to form 

 either nearly parallel series in the direction of growth, or 

 else more or less gyrating ridges ; {d) lastly, as the extreme 

 type, the papilla? rise as nipple- or nearly symmetrically 

 dome-shaped processes scattered more or less thickly over 

 the surface, but not arranged in radial series (fig. ob). 



(•4) The thickening reticulum undergoes a change in its 

 texture ; the threads w^iich bend up vertically become differen- 

 tiated from the rest of the elements of the reticulum and 



