32 GEOLOGICAL MEMOIRS. 



Gyllenhal, S.pomum always occurs in lower beds than S, auran- 

 tium ; at the Mosseberg ; on the island of Oeland near Bodahamn 

 (only S. aurantium) ; in Dalecarlia at Osmundsberg ; and one of 

 the species (^S. pomum) occurs near Boda and Wikarby, and at 

 Hallebraten in Nerike. In the Silurian strata of St. Petersburg 

 both species have been obtained, according to the Duke of Leucht- 

 enberg. 



The Sphaeronites may be looked upon as the type of the whole 

 family of Cystidea, for they are in all respects the most widely re- 

 moved from the crinoidal type. Most especially is there a total 

 absence both of any attempt at the development of arms and of any 

 law in the arrangement of the plates, while the spherical form per- 

 mitted the increase of growth to take place almost uniformly in all 

 directions from a central point, rather than confined it to a given 

 direction from below upwards, as in the Crinoidea. 



Genus CARYOCISTITES. 



Pelvis formed of four basal plates, two large and two srnalL Three 

 ranges of lateral plates rising one above another. 



3. Caryocistites granatum, Wahlenberg. \_Echinosph(Erites 

 granatum, Wahlenberg, Acta Soc. Ups. viii. 53. Sphceronites 

 testudiiiarius, Hisinger, Lethaea Suecica, p. 92. tab. 25. fig. 9. a.] 



Plate III. fig. 4. Plate IV. fig. 2. 



In this genus the plates are much larger than in Sphceronites, It 

 seldom happens that new plates are inserted between the old ones, 

 and the consequence of this is a greater regularity in the relation of 

 the separate parts. 



The pelvis (PL IV. fig. %p \^p 2) consists of four plates as in 

 Caryocrinites (see fig. 1), two of the plates adjacent to one another 

 (/? 1) being larger than the rest and forming irregular pentagons, 

 while the other two opposite to them (p 2) are four-sided. If how- 

 ever the larger plates are bisected we have six similar quadrilateral 

 figures, so that here also we may consider these larger ones as no- 

 thing more than pairs of smaller plates united together. The ova- 

 rial opening {b) is placed in the prolongation of a line drawn from 

 the stem through the intersection of the two larger plates. 



Six lateral plates (^) are placed on the edges of the hexagonal 

 base. In the intervals between them, and therefore alternating with 

 them, a second row of lateral plates (?') occurs, and again alterna- 

 ting with these a third row (5). A fourth similar series (t) forms 

 the summit. 



The ovarial orifice (i) is pentagonal, and generally rises above 

 the plates. The five valves with which it was closed are seldom 

 preserved. 



