VON BUCH ON THE YSTIDEA. 37 



rhombic plates, while the striation of the edges of the plate through 

 the middle of the smaller diagonal is entirely concealed. The plate 

 so delicately striated is generally somewhat elevated above the ad- 

 jacent ones, and in a line drawn from the pelvis upwards through 

 this vertical point and between the two finely striated rhombs we 

 find the mouth, which is distinctly elongated in this direction. On 

 each side of the mouth and still in the same direction, there is also 

 a very similar finely striated rhomb, which is formed from the lower 

 triangle of the hexagonal plate of the third order and the upper 

 plate of the second order, and is situated rather on one side between 

 the ovarial opening and the mouth. These five striae always termi- 

 nate with an opening which penetriites through the plate, and from 

 which doubtless ambulacra may have proceeded. 



It is worthy of notice, that a section made through the finely- 

 striated basal plate, the longer direction of the mouth, the ovarial 

 orifice and the longer diagonal of the basal rhomb, would divide the 

 entire animal into two symmetrical halves, which are always di- 

 stinctly compressed parallel to this direction, to which indeed the 

 singularly strong projection of the ovarial orifice may not a little 

 contribute. 



The elongated aperture which forms the mouth, and which is in 

 the direction of the ovarial orifice, is surrounded by what may be 

 called lips, consisting of a pouting forward of the plates which pro- 

 ject outwards near the mouth. Upon these lips and around them 

 may be seen five or six holes hardly larger than those upon the 

 lateral plates, whence ambulacra appear to have proceeded ; but 

 sometimes these holes are open towards the interior, the side or wall 

 in that direction being absent, and the appearance is then rather as 

 if the lips were bent forward towards one another. It is highly 

 probable that here also tentacula were protruded. M. Vollborth 

 has noticed and drawn these, and believes that he recognises in them 

 indications of arms as in Crinoidea ; but it would indeed be strange, 

 if, while everything else is so opposed to the Crinoidal type, there 

 should thus be a spot at which arms were inserted. But even if 

 this were so, we should not be justified in considering the present 

 genus as Crinoidean, were it only for the large ovarial aperture on 

 the side, which is not met with in the members of this latter family. 

 These tentacula may possibly have been covered with small plates, 

 like the proboscis of Hemicosmites and Spkcero7iiies, and this VoU- 

 borth's drawing induces us to conjecture. 



The large ovarial orifice occurs at the junction of four of the lateral 

 plates, two of them being of the first and the other two of the second 

 order. The middle stria? of each plate are elevated and swelled out 

 almost to a cylindrical form, so that the junction of these four semi- 

 cylinders forms the edge of the aperture and renders it quadrangular ; 

 but it happens occasionally, though seldom, that one of the plates is 

 absent and only three surround the opening. It is quite peculiar to 

 this genus, that the aperture in question is not, as in all the other 

 Cystidea, placed in the same (the upper) hemisphere as the mouth, 

 but in the lower half of the cup, nearly over the opening on which 



