of Edinburgh, Session 1870 - 71 . 
415 
4. On the Structure of the Palaeozoic Crinoids. 
By Professor Wyville Thomson. 
(Abstract.) 
The best known living representatives of the Echinoderm Class 
Crinoidea are the genera Antedon and Pentacrinus —the former the 
feather stars, tolerably common in all seas; the latter the stalked 
sea lilies, whose only ascertained habitat, until lately, was the 
deeper portion of the sea of the Antilles, whence they were rarely 
recovered by being accidentally entangled on fishing lines. Within 
the last few years Mr Bobert Damon, the well-known dealer in 
natural history objects in Weymouth, has procured a considerable 
number of specimens of the two West-indian Pentacrini, and Dr 
Carpenter and the author had an opportunity of making very 
detailed observations both on the hard and the soft parts. These 
observations will shortly be published. 
The Genera Antedon and Pentacrinus resemble one another in 
all essential particulars of internal structure. The great distinc¬ 
tion between them is, that while Antedon swims freely in the water, 
and anchors itself at will by means of a set of “ dorsal cirri,” Penta¬ 
crinus is attached to a jointed stem, which is either permanently 
fixed to some foreign body, or, as in the case of a fine species 
procured off the coast of Portugal during the cruise of the Porcu¬ 
pine in the summer of 1870, loosely rooted by a whorl of terminal 
cirri in soft mud. Setting aside the stalk, in Antedon and Penta¬ 
crinus the body consists of a rounded central disc and ten or more 
pinnated arms. A ciliated groove runs along the “oral” or 
“ventral” surface of the pinnules and arms, and these tributary 
brachial grooves gradually coalescing, terminate in five radial 
grooves, which end in an oral opening, usually subcentral, some¬ 
times very excentric. The oesophagus, stomach, and intestine coil 
round a central axis, formed of dense connective tissue, apparently 
continuous with the stroma of the ovary, and of involutions of the 
perivisceral membrane ; and the intestine ends in an anal tube, 
which opens excentrically in one of the interradial spaces, and 
usually projects considerably above the surface of the disc. The 
contents of the stomach are found uniformly to consist of a pulp 
