THE TTPPEE CHALK OP SOUTHERN SWEDEN. 



131 



than the pit beneath the transverse articular ridge, around -which 

 is a simple smooth surface. 



Size. Height 5 millim., greatest diameter 5 mm., least diameter 

 4 mm., greatest height of basals 1*5 mm., least height 1 mm., width 

 3 mm. 



As already pointed out by Prof. Lundgren, the stem-joints which 

 occur associated with this calyx are referable to three principal 

 types. It is, of course, possible that they belong to anothe" species 

 altogether ; but, like Prof. Lundgren, I am inclined to refer both 

 calyx and stem-joints to one and the same species. The question 

 cannot, of course, be decided until the Swedish collectors are fortunate 

 enough to meet with a perfect specimen. 



Type 1. Thin circular disks, about 3 millim. in diameter, with 

 faces perforated in the centre, but without markings of any kind. 

 They probably belong to the upper part of the stem immediately 

 beneath the calyx. Both in some forms of BourgueticriniLS* and in 

 Rliizocrinus the upper stem-joints have simple faces without any 

 of the characteristic sculpture which occurs lower down the stem. 

 The thin penultimate joint of Mesocrinus Fischeri (PL YI. fig. 1) 

 would seem to have been of this nature; and one can readily 

 imagine that in the larger M. suedicus the number of such simple 

 stem-joints was larger, as is actually the case in Bourgueticrinus. 



Type 2. The joints of this, the commonest type (PI. YI. fig. 3.), are 

 higher, with oval articular faces, the long axes of which are occupied 

 by transverse ridges. The planes of the ridges at the two ends of 

 each joint are inclined to one another at angles of from 60° to nearly 

 90° ; and the centre of each ridge expands considerably around the 

 opening of the central canal into a well-marked articular surface. 

 A median groove extends along each half of the ridge from the 

 central opening towards the margin of the joint-face ; and short 

 shallow branches proceed from it on each side so as to cut out the 

 upper portion of the ridge into a double row of small teeth. 



According to Prof. Lundgren these joints vary in size from 3 

 to 8 millim. in diameter, usually 5 or 6 millim. ; and their height 

 is about equal to their diameter. 



Type 3 (PI. YI. figs. 4-6). Wider but lower joints, the oval faces 

 of which are much more pointed than in those of type 2. They differ 

 very much in the proportion of height to diameter. In the thicker 

 ones (fig. 4) the expansion of the transverse ridge around the 

 opening of the central canal is very distinct, and there is a crescentic 

 pit on either side of it. But these features are much less marked 

 in the thinner joints, the faces of which are flatter (fig. 5), while the 

 transverse ridges scarcely expand at all around the central canal. 

 Some of these joints bear portions of the cirrhus-sockets, as already 

 pointed out by Prof. Lundgren. As in some species of Pentacrinus, 



* This is certainly the case in several specimens that I have examined, some 

 of which, contained in the University collection at Berlin, were kindly shown 

 to me by Prof. Beyrich. On the other hand, Quenstedt figures a top stem- 

 joint of B. ellipticus with a distinct transverse ridge and articular facet on its 

 under surface (Petrefactenbmde Deutschlands, Band iv. tab. 104, fig. 76). 



