NO. 1846. ON CERTAIN ELEVTHEROZOIC PELMATOZOA—KIRK. 109 



excessive weathering, and such being the case it seems periiaps 

 preferable to explain them on that basis. One would think that the 

 development of the arms of this form is quite sufficient to enable 

 the crinoid to use them as swimming or ambulatory organs and so 

 obviate the necessity of maintaining a purely passive existence. 



TYPE 4. 



This group has been erected for the reception of two blastoid 

 genera, Eleutherocrinus and Zygocrinus, and two cystid genera, 

 Protocrinus and Lichenoides. This division obviously contains a 

 rather heterogeneous collection of Pelmatozoa, all of wliich, however, 

 have a similar arrangement of proximal plates as regards the closing 

 of the apical aperture. In each of these genera the axial canal is 

 closed by an increase in the size of the plates composing the proximal 

 circlet, which become closely united but not fused. In this they 

 agree with Scyialocrinus, described above, and wath certain Agassizo- 

 crinus in which fusion of the infrabasals has not become effective. 



LicTienoides . — Lichenoides, which has been described and figured 

 by Barrande (1887) as well as the preservation of the material 

 permits, must have lost its column at a very early stage in its develop- 

 ment. As will be seen by reference to Plate 11, figure 11, the proxi- 

 mal circlet of plates is somewhat disarranged, and by a mutual 

 adjustment of the elements the apical opening is closed. 



Bather (1900) holds that the theca is "composed of rounded plates 

 of very different size, but semiregular in arrangement. At the base 

 are five to twelve minute plates." It seems to me that the cup is 

 composed of four circlets of plates, \vith five plates in each range, as 

 in Ma crocy Stella, to which this genus appears to be closely related. 

 The apparent irregularity of arrangement is due to a sliifting of the 

 plates subsequent to detachment from the column. 



The systematic position of this genus is liighly problematic. As 

 stated imder the discussion of Macrocystella above, the forms seem 

 more closely related to the Crinoidea than the Cystidea, and might 

 well be styled ''tricyclic" Crinoidea. At all events one finds con- 

 siderable difficulty in assigning them to the Cystidea. 



Protocrinus. — In the genus Protocrinus (PI. 11, figs. 12 and 13) it 

 may be seen that attachment by a column was had until compara- 

 tively late in the life of the animal — at least in certain individuals. 

 The specimen given as figure 12 apparently has four plates in the 

 proximal circlet, and there is a well-defined stem-cicatrix. By the 

 well-defined nature of the latter, it is evident that the column was 

 comparatively well differentiated. In figure 13 aU traces of stem 

 attachment have disappeared. There has likewise been a fusion 

 between two of the elements of the proximal circlet. 



