of the Onnoidea braohiata. 395 



among tlie non-pecluncnlated and later Crinoids tliat the re- 

 markably isolated genus Marsupites is characterized by the 

 circumstance that the five segments of the second basal circle 

 surround a lafge pentagonal central plate in the same way as 

 the segments of the first circle in Ciqiressocrinus'^ . 



For the sake of brevity, I will indicate the divided bases, ac- 

 cording to whether one or two circles are present, as monocyclic 

 or dlcycUc. With the dicyclic base it is sufficient to distinguish 

 the two circles as the upper and loAver, or as the outer and 

 inner, as has already been done in my memoir on Encrinus. 

 In that memoir, also, the reasons have been given which arc 

 opposed to the luialtered retention of the terminology adopted 

 by Johannes Miiller for the parts of the base. In this the 

 segments of the circle lying immediately upon the stem are 

 everywhere called hasalia — namely, both the segments of the 

 monocyclic base and those of the inner circle of the dicyclic 

 base ; the upper circle of the latter receives, as something 

 accessory, the special name of the jmrahasis. By this it is 

 implied that tlie consideration of the base should start from 

 the stem, and not, as is more natural, from the radii. Sub- 

 sequent autliors merely altered the names, without making 

 any improvement. Of the parabasal segments De Koninck 

 made pieces sous-radiales, from which resulted suhradialia^ 

 and, with Bronn, the subradial zone. But the monocyclic 

 base might with equal justice be named subradial. The name 

 of intcrradiaJs^ recently employed by Quenstedt for the para- 

 basalia, would, if adopted, be perfectly confusing. 



In many Crinoids the stem is of so simple a structure that 

 it only constitutes a transversely segmented appendage of the 

 calyx. This is the case with the stems having a circular 

 periphery, Avith a small round nutritive canal, and with inde- 

 finitely multiradiately striate articulating surfaces. From these 

 we must distinguish other stems which in various ways dis- 

 play a quinqueradiate structure in directions which stand in a 

 definite relation to the directions determining the arrangement 

 of the calyx. Sometimes it is by the pentagonally prismatic 



* Among the older Crinoids, F. Roomer's AstyJocrimis l^vis (Lethpca 

 Geognostica, Taf. 4'. fig. 13) appears, like Marsvpitcs, to possess two basal 

 circles, the lower ofwliich, however, does not surround a central plate, 

 but is attached to au undivided central boss, nearly as, in Apiocrimift, 

 the base is inserted upon the last joint of the stem. Ixoemer himself 

 regards the central boss as the base, and only assumes one basal circle 

 above it, which he calls the parabasis; but the arrangement of the lost 

 plates is not reconcilable with this view, as is shown by the figure 

 representing the corresponding plaster cast. The genus A4;/Iocn'»m 

 would be very different from A(/itssizocriium, if the preceding interpre- 

 tation is correct. 



29* 



