54 Mr. H. J. Carter on the close Relationship of 



granulation also extends. Small spines solid. Large spines 

 round and conical or compressed, elongated and wedge-shaped, 

 about l-25tli incli in diameter at the base, more or less regu- 

 larly distant from each other (fig. 11, a). Minute circular 

 apertures variable in size, but averaging l-257th inch in 

 diameter, thickly but not generally scattered over the surface, 

 being chiefly confined to the base of the large spines respec- 

 tively (fig. 11, 5), often connected by a small groove. Ver- 

 tical sections presenting traces of vertical tubes and chambers, 

 of which the former often contains an anuulated core (fig. 12, 5), 

 but no distinct lamination. Size of specimen horizontally 

 about 1^ inch in diameter ; vertical thickness about 4-12ths 

 inch. 



Hah. Marine, incrusting. 



Log. Upper Greensand, Haldon Hill, near Exeter. 



Ohs. This differs from the foregoing, viz. H. 'pliocena, in the 

 larger size and more compressed form of the large spines, 

 which are also arranged more regularly than those of H. 

 pliocena ; also in the distribution of the apertures on the 

 surface, which instead of being generally spread over it, are 

 chiefly confined to the bases of the large spines respectively, 

 where, when the spine is broken off" low down, they may be 

 seen to lead into tubes somewhat radiating round the base of 

 the spine ; also in the absence of the grooved branched reti- 

 culation so evident on the surface of H. fliocena^ while the 

 apertures may often be observed to be connected by a small 

 groove which seems to indicate the position of a coenosarcal 

 tube that once connected them, like that seen in some species 

 of Stromatopora (fig. 21). 



The situation of the apertures round the bases of the large 

 spines respectively resembles that seen in the living calcareous 

 species {H. calcarea), where they do not appear in the pit-like 

 "interstices;" also the compressed, wedge-shaped form of 

 many of the large spines ; while the irregular moniliform cast 

 or core of the vertical tubes coincides remarkably with the 

 same kind of mould presented by the vertical tubes in H. 

 pliocena. 



On what this specimen was based it is impossible to say 

 now, as its only form is that of a broad cone covering a shape- 

 less piece of solid, opaque flint of a whitish grey colour, which 

 was probably the form of the object on which it grew ; but 

 that it was laminated its thickness shows, although now there 

 is no trace of this lamination remaining, save in the presence 

 here and there of one of the chambers of the intervals with a 

 few of the small spines just projecting above its floor, as seen 

 in H. pliocena. 



