VON BUCII ON THE CYSTIDEA. 31 



having well-defined striae in the direction of the longer diagonal ; 

 and for this reason I shall describe such stria3 under the name 

 (rhombic) striae, or plications. They terminate towards the middle 

 of the plate by an aperture, which Pander considered to be a place 

 whence ambulacra were protruded, a view in which 1 have coincided 

 (Beitr. z. Best. d. Gebirgsform. in llussl. p. 27) ; and I have even 

 ventured to throw out the conjecture, that these striae may possibly 

 have been the borders of channels by which ambulacra parallel to 

 one another have been mutually conducted from one plate to the 

 adjacent one. But when these external striae are rubbed down, as 

 in the state in which the Sphceronites are generally found, so that the 

 true separating lines between adjacent plates can be distinctly traced, 

 we find on the surface no mark whatever of orifices or holes by 

 which they were pierced, as there must have been if these holes had 

 served for the passage of ambulacra, which could of course only 

 proceed from the interior. They are therefore entirely superficial, 

 and are probably only the terminations of covered channels or 

 hollow ridges along the length of the striae. In the Sphaeronites 

 which are found at Christiania in Norway, the striae are so promi- 

 nent that the rhombs which they form are sharply detached from 

 one another, and they completely conceal the line of intersection of 

 the true plates. In this state they have been improperly described 

 as belonging to Echinosphcerites (jranatum. They are figured by 

 Hisinger in the ' Lethaea Suecica ' (tab. 25. fig. 8). 



2. Sphaeronites pomum, Hisinger. \_v. Buck, Beitr. z. Best. d. 

 (jcbirgsform. in Bussl. i. 15. 16. according to Gyllenhal. Hi- 

 singer, Leth. Suec. tab. 25. fig. 7.] 



There is still considerable doubt with regard to this species. In 

 shape and in the distribution of the openings it differs very little 

 from *S'. aurantium \ for notwithstanding (Jyllenhal's statement, that 

 the anal aperture is so near the mouth that the two are often con- 

 fluent, this after all can only be an individual peculiarity, since other 

 specimens exhibit the two openings perfectly distinct. The ovarial 

 pyramid also, which Gyllenhal could not find, is not absent in this 

 species, since the Duke of Leuchtenbcrg has descril)ed and figured 

 it with perfect distinctness (Beschr. ein. Thieirest(;s d. llrvv. j). 2'5. 

 tab. 2. fig. 19). The essential difference between this spccicis and the 

 former is in the pores of the plates, two being observed on S,]}omum 

 which are connected by a small furrow, and which are not merely 

 superficial, but penetrate the plates and may be distinguisluid on the 

 stony nucleus. From ten to twelve little series of this kind occur 

 on each plate, and th(^se also have been noticed by the Duke of 

 Leuchtenberg, who has described them as occurring on a specimen, 

 perhaps the largest hitherto found, measuring thret; inches in dia- 

 meter. 



Sphaeronites have not been found except in nortlnirn latitudes. 

 They occur in Norway near Christiania ; very abundantly at Westra- 

 plana near the KimiekuUe, in West Gothland, where, according to 



