14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 76 



haps coincident with the decrease in size, the infrabasal ring was 

 ehminated. Such a modification as this would be no more remarkable 

 than the change from the massive, protruding base of Mycocrinus 

 to the flat and thin basal disk of Catillocrinus. And we have striking 

 examples, as shown in my work on the Crinoidea Flexibilia, pp. 119, 

 269, 277, etc., of the disappearance of infrabasals in individuals and 

 in species, in Ichthyocrinus and other Flexibilia, due to atrophy in 

 forms where, as in this case, almost the entire base is buried under- 

 neath the column. 



In the Permian member of the family, Paracatillocrinus, as de- 

 scribed by Professor Wanner, the basal ring appears usually to con- 

 sist of two unequal plates (in one specimen only a single suture is 

 .seen), as is the case in some, but not all, specimens of the Devonian 

 Mycocrinus. I very much doubt if that was the primary arrangement 

 in any of them, but believe that the apparently unequal division into 

 two plates is rather due to unequal fusion, as is shown by the fact 

 that in some specimens of Mycocrinus the base is completely fused, 

 in some divided unequally by two sutures, and in one by two distinct 

 sutures with a third one present but obscure. 



I have given the facts a^ T find them after a careful study of the 

 excellent material now assembled, corroborated by the observation of 

 a colleague of much experience in this kind of investigation. They 

 present a condition difl^erent from what I formerly supposed, and 

 which can only be interpreted as one in which, in a greatly specialized 

 type, along with other departures from the usual habitus of the 

 crinoids, there arose such a degree of instability of the base as to 

 allow it to become dicyclic or monocyclic within the same genus; to 

 be composed of 2, 3 or more plates ; or to be entirely undivided. 

 Wanner's studies on the Timor form (Perm. Echinod. Timor, p. 8) 

 led him to the conclusion that the number of basals is not constant 

 within his genus, or even within a species under it, and is therefore a 

 character of only secondary importance. 



The extreme flatness of the base, and thinness of its component 

 plates, as exhibited in Catillocrinus tennesseeae, does not continue in 

 the succeeding species, after C. turbinatus. In C. zuachsmuthi the 

 basal ring becomes somewhat, though still unsymmetrically, exposed 

 in a side view all around, and correspondingly thickened, as is shown 

 by a fractured specimen (pi. 3, figs. 9, 10) ; and in C. hradleyi and 

 C. carpenteri it increases farther until it occupies one-fourth to one- 

 third the total height of the cup. But in the Timor species, instead 

 of a further development in this direction, we find a reversion, not 



