108 MR. P. H. CARPENTER ON THE GENUS ACTINOMETRA. 



upper ends) to the lower surfaces of the five basals in the same way as the ligaments of 

 the arms are attached to the brachial segments, the fibres of the one passing gradually 

 into the protoplasmic basis of the other. The basals cannot, however, be regarded as 

 simply ossifications in this fibrous tissue of the same nature as the basal rays of Actlno- 

 metra ; for, as shown above, there is every reason to believe that they are developed, like 

 the other elements of the skeleton, out of the embryonic basal plates ; although, so far as 

 position is concerned, they are precisely homologous with the calcareous deposits within 

 the tendinous cords of the stem. 



On the other hand, the basal rays of Actinometra, which are similar in position, though 

 not in origin, to the peripheral portions of the basals of Pentacr'mus, are of the same 

 nature as the calcareous tissue of the leaf-like areas of the stem-segments, being simply 

 the result of the deposition of calcareous material around and between connective-tissue 

 fibres. 



In many of the fossil Articulate Crinoids the lateral union of the basals with one 

 another is so very complete that the lines of junction between them are not always 

 visible, and the "basis" has therefore been described either as entirely absent or as 

 replaced by the uppermost stem-segment, which, according to Midler's view, it is sup- 

 posed to represent. 



This is particularly the case in the Apiocrlnidce and in Eugeniacr'mus. Miller, who 

 was the first to describe the latter type l , mistook the first radials of E. caryophyllatus 

 for the basals, and described them as firmly anchylosed to what he supposed to be the 

 "superior columnar joint." Goldfuss 2 , however, rightly determined this last to be a 

 part of the first radials, which are very much prolonged downwards, while, at the same 

 time, he described the basals as replaced by the enlarged uppermost stem-segment, 

 which articulates with the inferior surface of the elongated first radials. E-cemer 3 did 

 not accept this view of Goldfuss's, although he recognized that the " superior columnar 

 joint " of Miller was simply a dorsal prolongation of the first radials ; but, like Miller, 

 he described these last as the basals. 



It is most probable that Goldfuss's view is the truer one, as in Hagenow's figure 4 of 

 Eugeniacrinus Eagenoicii, in which the first radials are not prolonged downwards as in 

 E. caryophyllatus, the piece on which they rest, representing that which Goldfuss called 

 the enlarged uppermost stem-segment of E. caryophyllatus, is seen to be distinctly com- 

 posite ; for its external surface is marked by five sutural lines, alternating in position 

 with those between the first radials, and evidently indicating the lines of union of five 

 basals. 



The "•eoloaical collection of the British Museum, which I have been able to examine, 

 thanks to the kindness of Mr. Henry Woodward, contains a very interesting series of 

 specimens from the Chalk which are labelled Apiocrinus elliptlcus. 



In some of them the basals form a complete ring, separating the radials from the upper 

 stem-joint, which is very much enlarged. But in other specimens the basals appear 



1 O+h cit. p. 111. - Petref. Germ. torn. cit. p. 102. 3 Lethoea Gcoguostioa, ii. Tbeil 4, p. 115. 



4 Min. Jabrb. he. cit. ix. p. 13. 



