30 GEOLOGICAL MEMOIRS. 



slender, and appears hardly adapted to support so heavy a weight 

 as is sometimes placed upon it : for this reason it would appear that 

 its length was not great, and perhaps in most cases the body of the 

 animal rested on the ground. In Sphccronites aurantiiun the diameter 

 of the aperture for the stem is only ^j^^th part of that of the rim of 

 the cup, but in Caryocijstites granatum^ Wahl., the proportion is 

 only one to fifteen, and in Cryptocriiiites cerasus one to seventeen. 



The species of Cystidea at present distinctly known and described 

 are the ibllowing :— 



Genus SPHiERONITES. 



1. Sph^ronites AURANTiuM, Hisinger. [ JV/as, Vet. Acad. Handl. 

 1740. tab. 11. fig. 18. Gyllmhal, Vet. Acad. Nya. Handl. 1772, 

 p. 242. tab. 8. fig. 4, 5. Wahlenberg, Acta Acad. Ups. viii. 52. 

 Pander, tab. 29. fig. 2, 3. Herz. v. Leuchtenb. tab. 2. fig. 17. 

 V. Buck, Beitr. z. Best. d. Gebirgsform. in Russl. tab. l.fig. 14.] 



Plate III. fig. 3. 



Form spherical, rising from a very thin round stem, with penta- 

 gonal nutritive canal ; six small plates form the pelvis ; these are 

 surrounded by other plates of larger and smaller size, which alter- 

 nate without any observable order and are very numerous, so that 

 one can count at least twenty upwards in a row. Most of these 

 plates are hexagonal, but many with seven, eight, nine or more sides 

 might easily be found. The mouth («), in a small proboscis sur- 

 rounded with plates, is placed diametrically opposite the insertion of 

 the stem (c). Lower down, but on the same hemisphere with the 

 mouth, occurs a large pyramidal orifice, closed with five or, more 

 rarely, six valves, which is the ovarial opening {h). On the top of 

 each of these valves is a small orifice piercing quite through the 

 valve, and possibly the eggs were extruded from these orifices, since 

 the valves themselves are never found open. In a direct line between 

 the mouth and this little pyramid, but quite close to the mouth, 

 is a small round anal opening, not elevated above the surface. 



The inequality of size and the minuteness of many of the plates, 

 and the way in which they are strewed over the surface, render it 

 probable that in this animal it was not only by additions to plates 

 originally formed tliat the whole increased in dimensions, but that 

 new plates were also constantly added, crowding in between the older 

 ones. 



The surface of each plate is covered with lines or striae, which are 

 at right angles to the edges of the plate. There are therefore as 

 many directions of these striae as there are sides of the plates, but 

 all meet in the central point, and this has been very well and clearly 

 described by Pander (tab. 29. fig. 3 «.). The striae of one plate 

 pass without any interruption or change of direction to the adjacent 

 one, and the two seem then to form but one, whose shape is a rhomb, 



