64 I. IJIMA : HEXACTINELLIDA. I. 



a row of isolated bristle-like spicules standino- out along the free 

 edge to a length of about 4 mm. In some specimens such 

 fringed lappets are not at all uncommon, while in others they 

 occur only occasionally and may even be entirely missing. 

 Rounded protuberances never exhibit the prostal spicules. 



The parietal ledges form a rather steep wall to the valley- 

 like, depressed spaces between tbem. These spaces are elongated 

 or irregular in configuration, — generally meandering and inter- 

 communicating, their shape depending upon the course taken by 

 the inclosing ledges. Some of the more extensive, depressed 

 areas may be said to have a comparatively flat surface. 



The parietal oscida, which do not exceed 2 mm. in diameter, 

 open on the depressed areas. Their thin edges lie nearly on a 

 level with the general surface of the latter. They are usually 

 found several to<>ether in the same area at intervals of 2-10 mm. 

 from one another. The distribution is on the whole irregular, 

 though often a number of them in succession are found iu a line, 

 the direction of which depends upon that of the long axis of the 

 depression containing them. Exceptionally, isolated parietal 

 oscula may open by means of a canal on the side or even on the 

 summit of the external ledge. In specimens which are still 

 actively growing at the uj^per end (figs. 3, 4), the openings are 

 in that region arranged more or less regularly in transverse and 

 longitudinal rows at short intervals. This regularity is however 

 lost as the development of parietal ledges advances in that region. 



The extremely delicate dermal latticework is, on close 

 examination, just visible to the naked eye, except on the more 

 elevated portions of the ledges, where the surface presents a 

 rather close-grained texture. The apertures into the incurrent 



