174 Clarl — Neiv Genera of Unstalked Crinoids. 



an external view. Dr. P. H. Carpenter's ^'Solaris group" of 

 '^ Actinometra,'' therefore, is seen to be identical with his 

 " Echinoptera group,' ^ provided tliat the other species agree with 

 C. pectinata in structure, which they probably do. In Comaster 

 I likewise found no syzygies proximal to the free arm ; l)ut here 

 the synarthries, extremely close as in Comatula, have secondarily 

 taken on a more or less irregular concentric or radiating, or a 

 combination of both, surface sculpture, which is never so perfect 

 as to conceal entirely the fundamental dorso-ventral synarthrial 

 ridge. This type of articulation, curiously like a syzygy, though 

 directly derived from the totally different synarthy, I propose 

 to call a pseudo-si/zygy . The Comasteridfe are now shown to 

 contain no exceptions to the rule that syzygies are associated 

 only Avith ohliqve muscular articulations, synarthries only with 

 straight muscular articulations, though Ave still have, as our now 

 single exception, the strange family Zj^gometridte. 



The large group Comatulida may be divided into three sub- 

 orders as follows: 



Comatulida Innatantes. 



PeliiKic coinatulids in which tlie basals are not metamorphosed but form 

 an intefrral part of the body wall ; the infrabasals are not united with the 

 central ])late, Init usually form part of the body wall ; occasionally, through 

 individual variation, they are al)sent; there is no evidence of attachment 

 at any stage, so tliat their central apical plate may possiljly represent tlie 

 dorso-central instead of the centro-dorsal of other comatulids. The plates 

 of the calyx, which is very large and more or less globular, are very thin. 



Included families. — MartiU])itid!L' ; Uinta('rinid;v. 



Comatulida Oligophreata. 



Bottom inhabiting comatulids, stalked when young; l)asals metamor- 

 plioscd into a rosette ; infral)asals unknown; cavity in the centro-dorsal 

 containing tlie ciiambered organ and overlying structures very small; a 

 well-develojicd ncm-ilcmma is present, at least in some forms; the disk is 

 more or less studdetl or I'ven completely covered with large calcareous 

 concretions or i)lates; the pimudes, at least the lower, are wholly or in 

 part prismatic, and are composed of short segments; the post- radial 

 series usually divide two or more times. 



Included families. — ComaMcridw ; ZiigomeindK ; Himcroviefridir ; 

 ColohoiiKtridu' ; Thala>iS())Ji('trid;c; TropioiDt'tridn'. 



Comatulida Macrophreata. 



Bottom inhabiting comatulids, stalkinl when young; basals usually 

 metamorphosed into a rosette; infrabasals liave I)een detected in two 

 species, where they fuse with tlie centro-dorsal; cavity in tlie centro- 



