REPORT ON THE CRINOIDEA. 21 



In one example of Pentacrinus cdternicirrus, which has a stem only 55 mm. iu 

 length, and rounded off at the twelfth node, the width diminishes gradually from above 

 downwards, though not to any very great extent. The same is the case in another 

 specimen with a stem 47 mm. long and rounded off at the eleventh node. In other 

 examples of the same type, however, the width of the stem remains uniform or even 

 increases slightly from above downwards. In a large specimen of Pentacrinus naresianus 

 the width of the stem, which is 5 mm. at the eighth node, is reduced to 3 "5 mm. by the 

 thirtieth node, which is rounded off below. 



In the young Pentacrinus ivyville-thomsoni represented in PI. XVIII. fig. 3, the stem 

 is 65 mm. long ; but it is not half as wide at the lowest (sixth) node as it is beneath the 

 calyx. It was described by Sir Wyville Thomson ^ as follows : — " The stem is 

 broken off in the middle of the eighth internode from the head. The lowest complete 

 internode consists of fourteen joints, the next of eighteen, the next of twenty, 

 and the next of twenty-six joints. There are eight joints in the cirri of the 

 lowest whorl, ten in those of the second, twelve in those of the third, and fourteen 

 in those of the fourth. This is the reverse of the condition in adult specimens, 

 in all of which the numbers of joints in the internodes, and of joints in the cirri, decrease 

 regularly from below upwards. The Ijroken internode in the young example and the 

 three internodes above it are all atrophied and undeveloped ; and suddenly at the third 

 node from the head the stem increases in thiclaiess and looks as if it were fully 

 nourished. There can be no doubt that in early life the Crinoid is attached, and that 

 it becomes disengaged by the withering of the lower part of the stem." ^ 



The diminution in the size of the stem is rather more gradual than is imphed in 

 the above description, for it commences at the head and extends regularly down to 

 the third node, where there is a more sudden change, as there is again at the fourth, 

 below which the diameter decreases but slowly. 



But it is in a very young individual of Pentacrinus decorus (PI. XXXV.), in fact 

 the youngest Pentacrinite that I have seen, that this downward tapering of the stem 

 and gradual diminution in the size of the cirri are most marked. The stem is a trifle 

 over 60 mm. in length, and has ten distinct cirrus-whorls apart from the very small 



1 On the Crinoids of the " PorcxTpiiie " Deep-Sea Dredging Expedition, Proc. Boy. Soc. Edin., vol. %'ii. p. 768. 

 Also in the Depths of the Sea, p. 445. 



2 The above description requires a little correction. The stem iu its present condition, as represented in PI. XVIII. 

 tig. 3, is broken at the top of the seventh internode, ivhich is certainly the one referred to by Sir Wyville as the eighth. 

 But its length is at least 5 mm. greater than as stated by him ; and the number of joints in the two lowest inteniodes 

 should be given as fifteen and seventeen, not fourteen and eighteen. They are di-awn correctly in the figure, 

 but the joints at the top of the third internode are not properly represented, as is also the case with some of the 

 cirri. The figures of this and of the other plates drawn for Sir WyviUe Thomson had been on stone for so long 

 when the stalked Grinoids came into my hands after his death, that I thought it better to let any errors remain 

 unaltered rather than to risk spoiling the plate by correctmg them. The description given of the cirri is also only 

 roughly accurate. Neither on the fourth whorl from the bottom nor anywhere else on the stem are there any 

 cirri with fourteen joints, even where the terminal claw is included ; though the regular decrease in the size of the 

 cirri from above downwards is very striking, as pointed out by Sir WyvUle. 



