406 



Prof. Beyrich on the Base (Pelvis) 



sometimes entirely concealed hy the stem. The quadriradiate 

 cross of the nutritive canal enters the pentagonal central plate 

 in the same position that it occupies in the quadrangular stem, 

 so that in any calyx with the vertical framework preserved 

 the directions of the five calycine radii may be easily com- 

 pared with those of the four stem-rays. The examination of 

 numerous calyces of Cnpressocrinus gracilis showed that in 

 the great majority the four rays of the nutritive canal occupy 

 such a position in the pentagon of the central plate that one 

 of the four rays is turned towards the left abjacent angle, and 

 the opposite one towards the middle of the right adjacent side, 

 whilst the direction of the two other rays is determined by 

 their crossing at right angles. 



In the following figure the two pentagons of the outer basal 

 circle and the central ])late 

 are placed one Avithin the 

 other, and the above-described 

 position, which is to be re- 

 garded as normal, is given to 

 the cross in the central plate. 

 The outline of the four-sided 

 stem, as it appears on the 

 lower surface of the calyx, is 

 added. 



Such a position of the cross 

 does not correspond with the 

 position of sutures by which 

 the pentagon of the central 

 plate might be broken up 

 symmetrically into four parts ; it would therefore also not be 

 possible in a stem the rays of which were in isomeral position 

 to the segments of a divided 

 inferior basal circle. But if 

 we draw in the pentagon of 

 the central plate, as shown in 

 the annexed figure, four su- 

 tures crossing each other at 

 right angles, to which the 

 four rays of the nutritive 

 canal stand in an antimeral 

 ■ position, we have the divi- 

 sion which Avould occur in a 

 dicyclic base which is divided 

 into four parts in accordance 



with the same axis as the monocyclic base of Melocrinus. 

 The four segments have the same position as in the lower 



