THREE NEW SPECIES OF METACRINUS. 441 



100. There are over 100 joints above the suprapalmar axillary, all of them with raised 

 distal edges. This character is not specially prominent on the later joints, but is very 

 well marked on the outermost radials and on the lowest arm divisions. 



Primary arms usually of 4-6, but in one case of 10 distichal joints. 7-10 palmars in 

 the secondary arms. Tertiary arms usually of 14-16 (rarely 12 or 18) joints, with 

 another axillary after 16 or IS (rarely 12, 20, or 22) joints on the outermost of each pair 

 of quaternary arms. The third joint after each axillary is a syzygy ; and the second 

 syzygy in the free arms may be anywhere between the thirtieth and sixtieth brachial. 

 Others follow at intervals of 8-20 joints. 



The radial, distichal, and palmar pinnules are all large and styliform, especially the 

 two latter. That on the second radial has two large and cuboidal basal joints ; but the 

 following ones become rapidly smaller and much flatter. 



The first distichal pinnules are much longer again, and consist of nearly 30 joints, of 

 which the basal ones, including even the first two, are much flattened laterally, though 

 of considerable depth. The following ones are of about the same length, but have wider 

 and more massive basal joints. After the first palmar pinnule the size gradually dimi- 

 nishes, rapidly at first, and then more slowly, while the pinnules become more flattened, 

 though the enlargement of the basal joints is visible for some distance out into the arms. 



The disk is paved by small irregular plates, which are not very closely set; but the 

 ambulacra are well protected by plates. The brachial ambulacra are limited to the 

 centre of the arm-furrow, and more or less differentiated on the pinnules into side- and 

 covering-plates. Colour in the dry state, a light purplish grey, with a greenish tinge on 

 the tips of the pinnules. 



Sab. Singapore. 



This magnificent specimen is the largest Metacrinm. and, in fact, the largest recent 

 Pentacrinite that I have yet seen. Few species have a stem exceeding 5 millims. in 

 diameter. It reaches 7 millims. in Pentacrinus asterius and Metacrinm nobilis; but the 

 stem of M. superbus is considerably wider than that of either of these two types. The 

 former is the only one which at all approaches it in the number and stoutness of the 

 cirrus-joints, as also in the frequency of the ray-divisions. 



The number aud very regular grouping of the free arms in Metacrinm superbus is a 

 somewhat striking character. Palmars appear to be universally present, so that there 

 are 40 tertiary arms ; and, with one exception, all of them which are preserved, either 

 wholly or partially, divide in the same way. Each of them has a suprapalmar axillary ; 

 and of the two arms which this bears, the outer, except in one case, divides again ; so 

 that each palmar axillary bears 6 arms : 2, 1, 1, 2. If this arrangement extended all 

 round the disk, there would have been 4 x 6 or 21 arms on each ray, making a total 

 of 120. 



It is exactly the same arrangement as often occurs on the distichal axillary of Penta- 

 crinus asterius, which has 12 arms to the ray; and also on the radial axillary of P. 

 Mulleri, P. Maclearanus, and P. Wyville-Thomsoni, It is of some interest, as affording 

 a clue to the mode of development of the armlets of the Jurassic Extrv.crinus, as 1 have 

 explained in the ' Challenger ' Report. 



