270 Field Columbian Museum — Geology, Vol. II. 



ent enough in the figures, but which may possibly be due to indivi- 

 dual variation, or abnormal development. The form and distribu- 

 tion of the compound radials differ from those observed in any of 

 the other genera of this group in the presence of two large plates 

 underneath the superior part of one radial, so that we have appar- 

 ently three infer-radials, with only two super-radials. The space 

 occupied by one of these in the calyx wall is enough to account for 

 the lateral bulging which gives its unsymmetrical form. Having 

 but the one specimen, we cannot tell whether this feature is constant 

 or not, and the specific and generic definitions do not depend upon 

 it. As asymmetry is a frequent character in this group, however, 

 there is no inherent improbability that the same construction will 

 be seen in other specimens, if such are found. We give for compar- 

 ison diagrams of Pisocrinus and Haplocrinus, the two genera nearest 

 related to this structurally, (PI. LXXXI, Figs. 7 and 8). 



Pisocrinus has two short super-radials, which rest upon one large 

 infer-radial in common. Haplocrinus has three short super-radials 

 each with its corresponding infer-radial. Our crinoid has two short 

 super-radials, one connected by a transverse suture with its infer- 

 radial, while the other is angular below, and meets the upper sloping 

 faces of the two infer-radials. If now we examine the diagram of 

 Haplocrinus (Fig. 8) we will see that the right anterior super-radial 

 is angular below, and meets by one side an upper sloping face of the 

 infer-radial below it, and by the other a corresponding sloping face 

 of the anterior radial, which is one of the two largest plates in the 

 calyx. If a portion of this anterior radial were cut off by a curving 

 suture, as indicated by the dotted line in the diagram, it would give 

 a construction substantially the same as that of our genus in this 

 respect, viz: two short super-radials supported by three infer-radials. 

 In view of the other pronounced differences in the composition of 

 the calyx, such a modification of the radial structure of Haplocrinus 

 may well have become constant in our form. 



A few of the arm plates have fallen in over the summit of the cup, 

 and are thus preserved. They are restored to position in the diagram 

 (Fig. 6). The first brachial of the left posterior ray is wanting, but 

 fts position is indicated by dotted lines. It will be observed that 

 the right posterior radial has a smaller facet, and bears a smaller 

 arm than the others. It is probable that the arms were very short, 

 with but few more brachials than remain in the right anterior ray. 



We cannot be absolutely certain that the orientation of the calyx 

 here given is correct, as we do not know the position of the anus. 

 It agrees with what we know of the relative positions of the com- 



