52 THE CEINOIDEA CAMEEATA OF NOETH AMEEICA. 



A permanent fixation of the Crinoids would perhaps restrict the geo- 

 graphical range of the species, whereas we know that some of them have 

 a very wide range. A majority of the species from the Lower Burlington 

 group at Burlington are found almost unaltered in the southwestern part of 

 New Mexico, and some in Arizona, and many species of the Keokuk group 

 have been traced from southern Iowa as far down as Alabama. And we find 

 in Scotland and eastern Russia, with but slight modifications, the same forms 

 which flourished in the Mississippi Yalley during the epoch of the Kaskaskia 

 group. 



B. Basals and Infrahasals. 



The base of a Crinoid consists either of one or two rings of plates, to 

 which the terms '^ basals " and " infrabasals " are applied. In dicyclic forms, 

 the infrabasals constitute* the proximal ring of the calyx ; the basals the next 

 circlet above. The former are radially disposed, the latter interradially. 

 The plates of either ring are in contact laterally, except the basals in a few 

 species of Zeacriims and Calpiocrinus, where the truncated low^er angles of the 

 radials, and occasionally the radianal, reach down to the infrabasals. The 

 basals are followed directly by the radials, except in the Acrocrinidse, in 

 which they are separated from the latter by a belt of auxiliary pieces, which 

 occupy a large part of the dorsal cup. 



The term "basals" was applied by the earlier writers invariably to the 

 proximal ring of the calyx, and when there were two rings, the plates of the 

 upper one were called '^subradials" by some authors, while others called them 

 '' parabasalia." To Dr. P. H. Carpenter '^ belongs the credit of having been 

 the first to point out that in dicyclic Crinoids the so-called "subradials" — 

 and not the proximal ring — are the homologues of the basals in the mono- 

 cyclic base, and that the lower ring in the dicyclic forms is an additional 

 element in the calyx. He demonstrated that from a morphological point of 

 view the same set of plates cannot be interradial in one genus, and radial in 

 another, and he considered the basals, which alternate with the radials, to be 

 the representatives of the genitals in the Urchins. The force of his argu- 

 ment has been generally acknowledged, and the American authors writing 

 since 1879 have adopted Carpenter's method, with the exception of S. A. 

 Miller, who still clings tenaciousl}^ to the old terms. Carpenter called the 

 plates of the proximal ring " under-basals," for which the term " infrabasals " 



* "Oral and Apical Systems of EcWnoderms." Quarterly Journ. of Microscop. Sci., Yol. VIII., 

 pp. 351-383. 



