1885.] NATURAL SCIENCES OF PHILADELPHIA. 261 



two at least, and the number increases in proportion to the 

 increase of the radials, by means of which the lower series attain 

 gradually a dorsal position. 



D. The Anal Plates and Anal Tube. 



It has been a general practice to regard all plates of the 

 azygous interradius as anal plates. From a strictly morpholog- 

 ical standpoint this is not correct, as comparatively few of these 

 plates are connected with the anal aperture, although all of them are 

 more or less affected by it. Properly speaking, in analogy with 

 recent Crinoids. there is but one true anal plate, and the succeed- 

 ing pieces are either interradials, or they constitute parts of the 

 anal tube, which, in the growing animal, by the increase of inter- 

 radials, were incorporated into the test. The latter plates, as 

 representing parts of the calyx, which serve the same purpose 

 as the true anal piece, might be very appropriately distinguished as 

 "higher" anal plates, but unfortunately in many groups it is 

 almost impossible to separate them from the interradials. A 

 discrimination, however, should be made wherever it is prac- 

 ticable. 



In the Pentacrinoid larva of Antedon rosacea, according to Dr. 

 W. B. Carpenter (Philos. Trans. Royal Soc. London, pp. 726— 

 747), the anal plate makes its appearance almost contempo- 

 raneously with the first radials, and stands on a level with them. 

 It is at first a rather irregular plate, which somewhat later takes 

 an elliptic form, and is gradually lifted out from between the 

 radials, and developed into a conspicuous funnel, which disap- 

 pears at the end of Pentacrinoid life, being removed b} r resorption. 



The earlier stages of the anal plates in the Palseocrinoidea are 

 onty known from phylogenetic evidence, but this shows that the 

 modifications which they undergo in palreontological times cor- 

 respond closely with those of the growing Pentacrinoid. In the 

 Inadunata, which have closer analogies with the Neocrinoidea 

 than the other two groups, and which like them have but a single 

 anal plate, the latter can be traced from its first appearance in 

 the Silurian to its total resorption in the Carboniferous and 

 Trias, and the various conditions of development, as thus repre- 

 sented, form excellent characters for generic distinction. Among 

 the earliest Inadunata, however, we find a transition state which 

 either is unrepresented, or has not been recognized in the Penta- 



