KARAKORAM STONES, OR SYRINGOSPHyERID^l. 7 



The relative size of the radial and interradial series is apparently of specific impor- 

 tance. 



In the radial sections the pores are seen to be spaces surrounded by interradial tubes, 

 some of which open on the floor. 



But in the radial sections of those types which have a great number of radial series and 

 a very scanty surrounding reticulate tubulation, the appearances under the microscope are 

 not so striking as in the other instances. In these the radial cone is very long, and bifurca- 

 tion occurs comparatively scantily, so that it is narrow, and the sides of the series often 

 appear to be parallel. The tubes of the radial series, moreover, are smaller than the sur- 

 rounding series ; they are not so close together side by side, and their course is almost invari- 

 ably straight. The interradial surrounding tubes are closer and larger than the others, and 

 they bend so as to present oval or geniculate knots, the continuity of the tube being often 

 lost to sight, a cross line denoting the upward or downward bend. They bend laterally also, 

 and touch here and there and bifurcate. The size of this series is usually larger than the 

 other, so that in these radial sections a radiating series of light lines is separated by broader 

 dark ones. 



This close structure is best seen in the group without pores, but it exists in the other, 

 in some species. (Plate III, Fig. 6). 



In one type of the SyringosphceridcB the pores are very developed, especially equatori- 

 ally. 1 In radial sections their presence is evident in the body or from the surface. They 

 extend in long rectangles one outside the other, and evidently bound radial series, but they 

 are situated just within the interradial. On either side of them are elongate tubes, off- 

 shoots of the environing series, and separating one space from another ; that is to say, from 

 within outwards is a bridge of cross and reticulate tabes parallel with the circumference, like 

 a tabula of a hydrocoral. Several of these bridges exist, and the last one is incomplete, 

 often quite at the surface where a pore is about to be occluded. 



In tangential sections, the circular outline of the pores may be seen surrounded with 

 tubes. 



In other specimens, this absence of tube-structure along definite lines, that is to say, 

 the presence of pores, is not so visible, but they can be detected as vacant pits or circular 

 spaces filled up with extraneous material. 



No special tubes enter the pores. 



The tubes forming both series are continuous, bifurcating, and inosculating ; and, as has 

 been already noticed, some are in the main straight and others are curved and form the 

 edges or sides of greater or less meshes or vacant spaces. 



The tubes are much larger in some types than in others, and they range from J^QQ inch 

 to 3-50 i nc h in diameter ; they usually retain the same caliber for some distance or altogether, 

 but frequently in some types they swell out, become varicose, flat, and again return to their 

 original cylindrical condition. (Plate III, Figs. 6, 8.) The union of tubes is by small 

 offshoots usually, but the bifurcation, often at an acute angle, gives origin to two tubes of 

 equal size to the parent, or nearly so. 



The tubes have a wall and a lumen, and the thickness of the wall varies ; moreover, 

 some of the constituents of it pass irregularly into the caliber, as well as occasionally sur- 

 round the tubes like a furry investment. 



1 Syringospharia porosa, Duncan. Plate III, Fig. 3. 



