Introduction to A nimal Morphology. 1 2 9 



(Comarocystis) ; anus always present ; there were five lateral 

 ovaries (?) with openings, when present, surrounded by five 

 plates, almost always present ; the pillar is short, jointed, or 

 none. About 80 species are known as fossils. Hyponome, from 

 Cape York, Australia — a small star-like free disc, ventrally 

 convex, with no calyx, and a dorsal scaly rosette — is the 

 nearest living ally, and approaches Agelacrinus.'^'' 



3. Crinoidea — stalked, at least in early life, with a cup- 

 shaped body of calcareous plates, with from 2-18, but com- 

 monly five, solid, primary, often branching, arms, independent 

 of the visceral cavity, except at the base, and furrowed longi- 

 tudinally above for the tentacle-like pedicelli given off by the 

 ambulacral tubes lying in these medial grooves radiating from 

 the mouth. This system seems purely respiratory. The 

 arms can move rapidly, and can close over the oral disc for 

 protection ; they have laterally articulated pinnules appended. 

 The ventral surface is, as in the last order, upturned ; the 

 dorsal stalked. 



The mouth is usually central, and in some fossil forms 

 mounted on a proboscis. The ciliated stomach winds around a 

 spongy calcareous spindle (compared to the lamina spiralis of 

 the Mammalian cochlea). The anus may be ventral, between 

 two water- vascular furrows, or absent (.^) (Holopus). The di- 

 gestive canal never extends into the arms. The pseud- 

 haemal system consists of a central sacculus giving off 

 branches to the arms. The ovaries are external, membranous 

 lamellge developed under the soft skin on the ventral surface 

 of the pinnae. The testes are similar, and the products 

 emptied by dehiscence. 



The column rises from a root-like disc, adherent to some 

 solid body ; sometimes several are rooted together. The 

 pillar itself consists of superposed calcareous joints, traversed 

 by a single or multiple axial canal. The joints are united by 

 ligaments and interarticular laminae of elastic vertical fibres, 

 and in some there are bundles of unstriped muscle-fibres 

 (none in Pentacrinus) ; here and there are whorls of jointed 

 cirrhi. The basement material of the calcareous plates is a 



* Chapman proposes an order Thyroidea for some forms which possibly 

 linked these to Asteroidea, ex. Edriaster. 



K 



