132 



P. H. CARPENTER ON TWO NEW CE1NOIDS EEOM 



two joints contribute to the formation of a socket, and the sockets 

 are at the ends of the long axes of the two apposed faces, so that 

 there were two cirrhi at each node, and at least three nodes in im- 

 mediate succession (fig. 6). The two grooves in the respective 

 transverse ridges form by their apposition a canal which lodged the 

 vessels proceeding to the two cirrhi from the central vascular axis of 

 the stem, and opened at the bottom of each cirrhus-socket *. 



In the absence of complete specimens of Mesocrinus suedicus it is, 

 of course, impossible to determine where these nodes or, rather, 

 groups of nodes occured in the stem, or even whether a stem of this 

 character was associated with the calyx under description. I suspect 

 that the verticils of cirrhi were limited to the wide lower part of the 

 stem ; but it is not possible to form any opinion as to whether they 

 were simple cirrhi like those of Pentacrinus, or irregularly branched 

 radicular structures like those on the lower stem-joints of Rhizocrinus 

 lofotensis. 



Failing direct evidence to the contrary, it certainly seems to me 

 most probable that the calyx and stem-joints fromKopinge all belong 

 to one species, which would then differ from Mesocrinus Fischeri in 

 other characters than those of the calyx ; for the lower joints of 

 M. Fischeri (PI. YI. fig. 1) are all much longer than wide, as in 

 Rhizocrinus, Bathycrinus, and the larval Antedon, and they rarely 

 bore cirrhi (PI. Yl.fig. 1). In this latter respect M. suedicus must have 

 been related to M. Fischeri much in the same way as Rhizocrinus 

 lofotensis with abundant radicular cirrhi on the lower part of its stem 

 is related to R. Rawsonii t which had " very few radicular cirrhi." 



The wide lower stem-joints of M. suedicus (PI. YI. figs. 4-6) 

 have much less resemblance to the corresponding joints of M. 

 Fischeri than to those of Bourgueticrinus ellvptieus, as represented 

 by d'Orbigny ; and they further resemble these last in having the 

 transverse ridge continuous across the articular face. In B. con- 

 strictus, however, the ridge is interrupted in the centre, and the 

 more or less marked excavations in the lateral portions of the joint- 

 face are connected with one another round the central canal, very 

 much in the same manner as the two cornua of the grey matter 

 unite around the central canal of the spinal cord This feature is 

 also distinctive of Rhizocrinus and of the Antedon-larva, § ; and in 

 both of these types the transverse ridge is cut up into a double row 

 of minute teeth. So far as I know, this character has never been 

 described in any species of Bourgueticrinus ; and Geinitz neither de- 

 scribes nor figures it in Mesocrinus Fischeri, though (as mentioned 

 above) it occurs in M. suedicus. 



* Quenstedt (op. cii. p. 368) has described cirrhus-sockets on stem-joints from 

 the "White Chalk of Eiigen, and has remarked that the grooves in the trans- 

 verse ridges of these nodal joints are often very distinct ; but there seem to 

 have been more than two cirrhi at each node (tab. 104, fig. 63). 



t " Zoological results of the Hassler Expedition. I. Echini, Crinoids, and 

 Corals," Illustr. Catalog. Mus. Comp. Zool. at Harvard College, no. viii. p. 27. 



J This seems to be also the case in the so-called B. cllipticus from the Eocene 

 of Traunstein (Quenstedt, op. cit. iv. tab. 104. fig. 82). 



§ Sars, ' Crinoides vivants,' pp. 5, 6, pi. ii. fig. 27, and pi. vi. fig. 17. 



