1869.] MEEK AND WORTHEN — ON PALEOZOIC CRINOIDEA. 441 



the tissue of the softer parts of its alimentary canal, we may infer 

 that this convoluted organ was, as it were, a kind of frame work, 

 secreted for the support of the digestive sack, which was probably 

 more or less convoluted in the same way in many, if not all of the 

 Palsezoic Crinoids, though not apparently, in all cases, endowed 

 with the power of secreting a sufficient dense structure of this 

 kind to leave traces of its existence in a fossil state. 



So far as we are at this time informed, this organ has yet been 

 very rarely observed in any other family than the Actinorrinidce, 

 though it was probably more or less developed in various other 

 groups. In one instance Mr. Wachsmuth found it in a Platycri- 

 nus, but here it seems to be, in the specimen found, merely a 

 spongy mass, not showing very clearly the convoluted structure. 

 Some traces of what was supposed to be something of this kind 

 were also observed by him in onb of the Blastoids. 



5. Ambulacral canal passing under the vault in the Acfino- 

 crinida;. In the third and fourth Decades of descriptions and 

 illustrations of the Canadian Organic Remains, Mr. Billings, the 

 able palasontologist of the Geological Survey of the Canadian 

 provinces gives some highly interesting and instructive remarks 

 on the ambulacral and other openings of the Palaeozoic Crinoids. 

 In these remarks he noticed, at length, some striking differences 

 between the vault, or ventral disc, of these older types, and that 

 of the few living examples of this extensive order of animals. 

 That is, he noticed the facts, that while in the living Comatula and 

 Pentacriiius, the ambulacral canals are seen extending from the 

 arm-bases across the surface of the soft skin-like ventral disc, to 

 the central mouth, and these genera are provided with a separate 

 anal opening, ^'ituated excentrically between the mouth and the 

 posterior side, that in the Palaeozoic Crinoids the ventral disc is 

 very generally, if not always, covered by close-fitting, solid plates, 

 showing no external traces whatever of ambulacral furrows 

 extending inward from the arm-bases ; and that in nearly all cases 

 they are merely provided with a single excentric or sub-central 

 opening, often produced into a long tube, which, like the vault, is 

 made up of solid plates. He showed that there is no evidence 

 whatever that the ambulacral canals, in these older types, were 

 continued along the surface of the vault from the arm-bases to the 

 only opening, whether sub-centrally or laterally situated, and that 

 in cases where this opening is produced in the form of a greatly 

 elongated proboscis, or tube, such an arrangement of the ambula- 



VOL. lY. D Fo. 4. 



