48 ^Ir. IT. J. Carter on the close Tielntionship of 



In outward tbnn the large spines, Avhieli average -rV iiich in 

 height, resemble the small ones in being serrate, with the 

 points of the teeth directed upwards (fig. 1, </) ; but in a ver- 

 tical section of the whole skeleton they will be found to be 

 based upon a number of the smaller spines of the first or basal 

 lamina, which, like the rest, become lost in the general reticu- 

 lation of the skeleton before the latter rises upwards into the 

 large conical spine mentioned. This spine consists of a scries 

 of serrulated longitudinal ridges corresponding with the hori- 

 zontal radial terminations of its internal network (fig. 2), and, 

 diminishing in number from several ridges at the base as tliey 

 slope inwards and upwards, are finally reduced to three or four 

 at the summit, which, by the union of the remaining ridges 

 there, thus becomes closed (fig. 2, a) ; so that the whole some- 

 what resembles a pinnacle of open gothic architecture which 

 is in direct communication with the skeleton below, where, as 

 before stated, it thus becomes based on pillars which were 

 once the small spines of the first or basal lamina. 



Hence, if a horizontal section be made near the summit, it 

 will represent a stellate form in which the rays or ridges 

 apjiear to radiate from a solid axis (fig. 2, a) ; while, a little 

 further down, a similar section will present a hollow axis in 

 comnmnication with the reticulate stmcture of the spine, which 

 also finally terminates in the ridges on its surface (fig. l,,^', 

 and fig. 2). Thus t\\^ i^oint of the larger spine is solid and 

 the body hollow-reticulate. 



In short, if projected on a plane surface, the greater number 

 of ridges at the circumference reduced to three or four at the 

 summit would represent the septa of an asteroid polyp-cell in 

 a stony coral, whose intervals, in like manner, flowing from 

 two or three gutters at the summit, and branching out towards 

 the circumference, would also be stelliform — a circumstance 

 w^hich it might be well to remember, as it seems to be repeated 

 under another form in Stromatopora^ where the summits 

 appear sometimes to be solid and sometimes hollow, according 

 to the position of the section, but always with an asteroid 

 or stellate appearance. 



The large spines are thickly scattered over the surface 

 among the small ones at short but irregular distances, and are 

 only found fully developed or largest on those parts of the 

 Buccinum which are not exposed to friction by the Pagurus 

 (by which the shell is on such occasions almost invariably 

 tenanted) dragging it over hard objects at the bottom of the 

 sea. 



Lastly, on the surface of the skeleton may frequently be 

 observed a branched reticulation formed of coenosarcal tubular 



