96 



gent collector and dealer in fossils, to whose zeal and integrity in collecting and 

 preserving all Crinoidal remains which fell under his observation, I am much 

 indebted for acquiring a series of highly illustrative specimens. 



/ 

 Description. 



The COLUMN (PL. i. fig. 1. PL. vi. fig. 1. to 22.) of this animal, is near 

 the pelvis formed of very thin joints, alternately a little longer and thicker, with 

 a still larger one intervening every second or third joint. This regularity is in- 

 terrupted further down by the intervention of four or five small joints, all ap- 

 pearing muscular, and as if they had not yet acquired solidity b y the secretion 

 of calcareous matter, which I consider as a proof of the formation and interpos- 

 ing of new joints during the life of theanimal between those already existing. 

 Still lower down the column the joints become of a more uniform thickness 

 and size, and vary but very little. In an early stage of growth they are ex- 

 ternally much contracted near the margin of adhesion, thence somewhat moni- 

 liform, which form is continued when they increase in size, though less conspi- 

 cuously showing itself, sometimes only in a slight central elevation. The arti- 

 culating surface of the joints (PL. vi. fig. 1.3. 5.) is very regularly striated or 

 grooved in radii, from the middle, producing externally a most regular and 

 beautiful suture of mutual insertion. (PL. vi. fig. 15.) Near the centre they 

 are excavated on both sides, forming a muscular edge, which surrounds the ali- 

 mentary canal. In sections we may sometimes see the alimentary canal of a 

 considerable size (PL. vi. fig. 14. and 16.) and not unfrequently observe it at 

 regular intervals more or less alternately contracted and dilated, yet always 

 leaving a large passage open. It is from the increased size of the alimentary canal 

 in columns of larger diameter, that I apprehend the epidermis or periosteum, 

 whose usual office was to secrete the calcareous matter forming the joints, had 

 also the power of absorbing and removing it ; for, without this, the passage for 

 the alimentary canal could not be enlarged, unless we indeed could admit that 

 the induration of the calcareous matter forming the joints did not take place till 

 the animal was full grown, which, however, is quite contrary to the operations 

 of nature in the other Crinoidea. 



The COLUMN (PL. vi. fig. 17. to 22.) sometimes exhibits a swelling out of 

 several joints, which renders it barrel-shaped, and a lateral concave depression 

 with a central perforation as noticed in Poteriocrinites crass us, page 69. 



