ID ki i.i.ki i\ 82, i \i i BSD BT.Vi Ks \ vnnv-u, MisEl'.M 



In id additional specimens in the Copenhagen Museum the first pinnule is on the 

 right of the Becond brachial to 50 oases, and on the Left to 48. Gisl6n said that it 

 mighl be supposed this peculiarity might be accounted for by the genus being 10- 



d; but the same distribution may also be seen to the 5-rayed young. In Thau- 

 matocrinua renovotua 1\ appears to the right of the second brachial in three cases and 

 i,, the left to two. The position of 1', also varies to a young individual of T. jungerseni. 



In Pentametrocrinu8 and Aiopocrinus the first Byzygy is usually between brachials 

 4 + 5, and the first pinnule is on either the second or the fifth brachials. 



Carpenter said that to Peniametrocrinua japonicus the lowest pinnule (on the 

 fifth brachial) appeared to the right to 11 cases out of 12. Pi also appeared to the 

 right on the- second brachial to P. oariams. It is also stated to be commoner on the 

 righl than on the left to P. semperi. Gislen examined two specimens of P. diomedeae; 

 in these the Lowest pinnule was on the right in 9 cases out of 10. Judged from Koehl- 

 er's figures the same seems to be the case in P. atlanticus. In Aiopocrinus sibogae P, 

 in 1 oases out of 5 is to the right on the second brachial. 



Gislen gave some examples of the suppression of a right or a left arm in other 

 coxnatulids. The examples given showed a tendency for the suppression to be located 

 differently to certain oligophreate families on the one hand and certain macrophreate 

 t\ pes on the other. 



In a '.'-armed specimen of Comatula pectinata from Java the left arm, as in Eudio- 



18, is rudimentary. It is represented by a small calcareous lump of two ossicles 

 united by sy/.ygy. The right arm has the first 6 brachials united in 3 syzygial pairs. 



Springer described a 9-armed specimen of Uintacrinus sociaiis in which a left arm 

 is suppressed into a pinnule. 



( iisl6n found a similar case in a 9-armed specimen of Antedon petasus. On the 

 undivided arm the second and third ossicles are united by synarthry, and the fourth 

 and fifth and tenth and eleventh are united by syzygy. The undivided arm is as stout 



B others. On both sides of the ami the first gonad is on the third pinnule. The 

 unusual distribution of nonmuscular articulations is the same as in the specimen of 

 alia just mentioned. According to Gislen these cases may be ex- 

 plained in two ways cither the reduction has gone so far that both the suppressed 

 arm and the ossicle to which it was attached have disappeared, or the arm alone has 

 ed, the IBr, and IBr 2 having been coalesced into a single ossicle. Since 

 there is a muscular articulation between the first and second ossicles following the 

 radial, the Becond alternative is believed by Gislen to bo the more probable. In one 

 uf these cases it is clearly a right arm and in the other a left arm that has been sup- 

 preesed. < rislen said it is to be desired that more data regarding the pinnulation of 

 similar forms with undivided postradial series should he made available in order to 

 .'liable us to decide whether the tendency to suppression is more frequent in one or 

 the '>thcr, or, as in Thoumotocrinus, equally frequent to both. 



Gislen noted that during ontogenetic development the first arm ramification is 



formed by two equally stout arms. Sometimes, however, it seems that a difference 



between the two arms which is very insignificant, and in the larger young 



soon disappears, arises, at least in certain cases. Thus we have here a difference in 



I ii between the two arms of a pair, not a difference between pairs of arms such as 

 is illustrated and described by Perrier. This last, indeed, seems not to occur. The 



