THE UPPER CHALK OF SOUTHERN SWEDEN. 



133 



One of the stem -joints of M. Fischeri which is figured by Geinitz 

 is very singular. There is a thick articular rim around the opening 

 of the central canal of the oval-oblong face, as in the lower stem- 

 joiuts of M. suedicus ; but the ridge proceeding from this to either 

 end of the oval is Y-shaped and not simple. Some of the stem-joints 

 of B. ellipticus and also of Platyerinus Icevis which were figured by 

 Miiler * present very similar characters ; but I have not found 

 them in any of the j oints of M. suedicus. 



The genus Bourgueticrinus is rather in confusion just at present, 

 all those stem-joints occurring in the Mesozoic rocks being referred 

 to it that have elliptical articular faces with transverse ridges upon 

 them, which are in different planes at the two ends of each joint ; 

 and we are unable to classify these joints properly in the absence of 

 sufficiently perfect specimens of whole individuals. 



In any case, however, the so-called Antedon Fischeri and its 

 Swedish ally have stem-joints closely approximating to the Bour- 

 gueticrinus type (PI. YI. figs. 3-6). Nevertheless the calyx is 

 quite different (PI. YI. figs. 2 & 7). Seen from the side it has a 

 certain resemblance to some forms of Millericrinus Munsierianus, 

 d'Orb., and of M. Nodotianus, d'Orb. But this resemblance dis- 

 appears altogether when the upper surface of the calyx is examined ; 

 for the central funnel of Millericrinus is very large, and the articular 

 faces of the radials which surround it are wide and low, barely 

 meeting laterally ; while Mesocrinus has quite a narrow central 

 funnel (fig. 7, a) and relatively high articular faces, which diminish 

 considerably in width towards their upper ends, but are in contact 

 for the whole length of their sides. 



On the whole the calyx most resembles that of a Pentacrinus, or 

 rather of that section of the genus with a closed basal circlet, which 

 is referred by de Loriol f to Gainocrinus. Had I either calyx alone 

 before me, I should certainly refer it to Pentacrinus, among the recent 

 species of which there is a considerable variation in the proportions 

 of the different parts of the calyx In Cainocrinus, Millericrinus, 

 Bourgueticrinus §, and Rhizocrinus, the composition of the calyx is 

 the same. In all these genera there is a closed circlet of five basals, 

 on which the five radials rest, just as they do in Mesocrinus. But 

 there are considerable differences among these five types in the nature 

 of the articular faces of the radials. In Millericrinus these faces 

 are very wide and low, and are nearly or quite separated laterally, 

 while the fossae for the muscles and interarticular ligaments are 

 usually but slightly developed ||. In Bourgueticrinus the articular 

 * Op. tit. pp. 34, 75. 



t 'Monographic des Crinoides fossiles de la Suisse,' Geneva, 1877-1879, 

 p. 111. See also "On the Genus Solanocrinus, Goldfuss, and its Eelation to 

 Recent ComatulEe," Joum. Linn. Soc, Zool. vol. xv. 



.\ Compare figs. 21 and 23 on pi. xi. of Journ. Linn. Soc. Zool. vol. xv., 

 with fig. 3 on pi. vi. of the Popular Science Review, new ser. vol. iv. 



§ In some specimens of " B. ellipticus" in the national collection at South 

 Kensington the basals appear externally as small triangular pieces which are 

 not in contact laterally. 



|| According to de Loriol, Millericrinus differs from Apiocrinus in the presence 

 of an articular facet on the first radials. In the latter genus " leur surface 



Q. J. G. S. No. 146. l 



