A MONOGRAPH OF THE EXISTING CRINOIDS 457 



The smallest specimens also have large basals that form a continuous ring visible 

 under the radial circlet. In the smallest specimens the radial circlet encloses the 

 whole visceral mass. 



All these primitive characters therefore persist rather late in this species. 



Gisl6n foimd the number of arms in 36 nearly full grown individuals to be as 

 follows: 10 (18 specimens), 11 (9), 12 (5), 13 (2), and 16 (2). He remarked it is rather 

 curious that the largest specimens often have only 10 arms while the multibracliiate 

 specimens have shorter arms. He said that a similar condition is also noticed in 

 Cyllometra pulckella { = manca, see page 137) and perhaps has something to do with 

 the catching of food (see Part 2, page 84, fourth paragraph). He noted that the length 

 of the distal pinnules, with some irregularities, follows the length of the arms: but it 

 shows great variability in specimens with an arm length of 70-90 mm. 



On the basis of his abundant material Professor Gisldn discussed the status of 

 Asterometra lepida and A. acerba, each described from a single specimen. He said 

 that A. lepida is supposed to differ from A. anthus and A. acerba by having a small 

 conical centrodorsal with smaller cirrus sockets and therefore presumably more slender 

 cirri. He noted it is a general rule that the apical cirri, formed at a younger stage, 

 are more slender than the proximal cirri, formed at an older stage. The more robust 

 the individual is the more robust are the cirri. This character is therefore not neces- 

 sarily very important if other features supporting the suggestion of a real difference 

 are not added. The form of the centrodorsal is subject to great variation. A speci- 

 men from Bock's station 53 with an arm length of 70 mm., and therefore of the same 

 size as the type specimen of A. lepida, has a small conical centrodorsal with relatively 

 small cin'us sockets. A specimen from station 59 with an arm length of 85 mm. is 

 transitional to another from station 59 with an arm length of 100 mm. the centrodorsal 

 of which is of the typical anthus-acerba form. As all transitions between the type of 

 centrodorsal fotmd in the single specimen of A. lepida and the form typical of A. 

 anthus occur Gisldn said he could not consider A. lepida as anything but a young 

 individual of A. anthus. With this conclusion I agree. 



Regarding the supposed differences between A. anthus and A. acerba Gisl6n said 

 that I differentiated the two by the following characters; in A. anthus (A) the distal 

 pinnules are 9 mm. long, (B) the outer segments of the distal pinnules are twice as 

 long as broad, (C) the dorsal brachial spines are long and strongly curved, (D) the 

 radials have a rounded tubercle, (E) the IBr series lack a median keel, and (F) the 

 arms are more than 10; whereas in A. acerba (a) the distal pinnides are 13 mm. long, 



(b) the outer segments of the distal pinnides are up to throe times as long as broad, 



(c) the dorsal brachial spines are blunt, short, and not much curved, (d) the radials 

 have a dorsoventrally elongated tubercle, (e) the IBr series have a faint, low, median 

 carination, and (f) there are 10 arms. 



In some of his specimens he foimd these characters mixed in the following manner; 

 in a specimen from Bock's station 56, A(a), B, c, D, E, F; in six specimens from 

 station 59, Aa, Bb, C, d, E, F; A(a), B, c, d, e, (F)f ; a, (B)b, C, D, E, f ; a, b, C, D, 

 E, f ; Aa, b, C, d, E, F; a, b, C, d, E, f; and in a specimen from station 53, (A)a, Bb, 

 Cc, d, e, F. 



From these examples, he said, it seemed evident that the characteristics of A. 

 anthus and A. acerba are irregularly mixed in the different individuals. He noted that 



724008 — 17 so 



