NATURAL SCIENCES OF PHILADELPHIA. 327 



of Structure, the finest laces that it is perhaps within the power of hunaan skill 

 to fabricate ; and as it is entirely free from any surrounding matrix, excepting 

 at one side below, the specimen has to be handled with great care, as a mere 

 touch of this delicate part would probably cause it to fall into hundreds of 

 minute fragments. On examining it under a magnifier, the little bars of which 

 it is composed are seen not to intersect each other at any uniform angle, but 

 anastomose, so as to impart a kind of irregular regularity, if we may so speak, 

 to the form and size of the meshes. Of these little bars there are two sizes, the 

 larger forming the larger meshes, while within the latter a smaller set of pro- 

 cesses extend partly or entirely across, so as to form more minute meshes ; the 

 whole presenting a beautiful appearance, of which it would be difficult to con- 

 vey a correct idea by a mere description alone, without the aid of figures. 



From analogy, judging from what is known of the internal structure of the 

 recent genus Comatala, in which several authors have noticed a reticulated 

 calcareous structure secreted within the tissue of the softer parts of its alimen- 

 tary 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 Palaeozoic 

 Crinoids, though not apparently, in all cases, endowed with the power of se- 

 creting a suflicient 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 Actinecrinidse, though it was probably 

 more or less developed in various other groups. In one instance Mr. Wach- 

 smuth found it in a Platycrinus, 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 one of the Blastoids. 



5. Ambulacral canah passing under the vault in the Actinocrinidx. In the third 

 and fourth Decades of descriptions and illustrations of the Canadian Organic 

 Remains, Mr. Billings, the able palajontologist 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 re- 

 marks 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 Pentacrinus, 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, 

 situated excentiically 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 j)lates, showing no external traces whatever of ambula- 

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

 cases they are merely provided with a single excentric, or subcentral 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 subcentrally 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 ambulacra would be 

 almost a physical impossibility. Hence he concluded that the ambulacral 

 canals must have passed directlj' through the walls of the body at the arm- 

 bases ; and he gave several figures of various types, showing ojjenings at the 

 base of the arms, through which he maintained that the ambulacra must have 

 passed to the interior of the body from the arms. 



Although these arm-openings had long been well known to all familiar with 

 our numerous types of western Carboniferous Crinoids, in which they are very 



1868.] 



