NO. 3 ON THE FOSSIL CRINOID FAMILY CATILLOCRINIDAE I3 



those previously described, I have inferred the composition of the 

 base, as seen from the dorsal side, consistent with the structure at 

 the inner floor, substantially as I have drawn it in figure 9 of plate 2. 

 The outline of the infrabasal ring is not sharply defined by lines and 

 angles, but is obtusely angular or rounded, as the basal ring itself 

 appears in the same specimens. Its appearance is not unlike that of 

 the base in dicyclic genera like Eupachycrimts, where the small 

 infrabasal cone is seen from the interior projecting at the end of a 

 deep funnel. 



In two other specimens an obtusely angular or rounded space at 

 the middle of the base is pushed inward from the dorsal side; it is 

 of the same size as the inner cone in other specimens, and looks as 

 if it had been separated from the surrounding basals by external 

 pressure, the central area in one remaining intact but depressed to 

 a lower level than the adjacent surface (pi. i, fig. 17). In four 

 others a similar space at the center of the base is broken out, but not 

 well defined (pi. 2, figs. 5, 6). It is evident that the infrabasal area 

 was a weak spot in this thin base, since that portion alone is broken 

 away in at least six specimens otherwise intact. 



Putting these facts together, we have as evidence bearing upon the 

 composition of the base in this species: Three specimens with the 

 plainly divided cone in place at the inner floor of the calyx, in one of 

 which the exterior boundary is clearly defined by fracture ; two in 

 which the space corresponding to it is displaced by external pressure ; 

 four in which it is broken out ; two polished specimens in which the 

 outline corresponding to the cone is seen from the dorsal side, and 

 at least four sutures connecting with it ; and the appearance at the 

 interior of more than three basals surrounding the cone. I find my- 

 self unable to explain this assemblage of facts except as proof that 

 in this species there is a dicyclic base, which, however much it may be 

 modified by fusion, consisted primarily of three infrabasals and five 

 basals, as originally described by Shumard. 



Whether such a set of plates at the interior exists in any of the 

 later species cannot be ascertained from the material available, but I 

 am certain that infrabasals do not appear at the exterior in any of 

 them ; and in view of the definite proof of a division of the basal ring 

 into three plates, as in C. zvachsmuthi and C. carpenteri, in which the 

 sutures are distinctly seen continuing to the axial center, I am of the 

 opinion that in those species the base consists of only the one ring of 

 plates. 



If that be true, it means that in the course of successive modifica- 

 tions of this type as represented in the American Carboniferous, per- 



