107 



Locality. 



Upper Bed, No. 1, and one of the lower Beds, No. 15, of Dr. BRIGHT'S 

 Series, distinguishing the Mountain Limestone formation along the River 

 Avon, near Bristol ; the Mendip Hills ; Mitchel Dean ; and the transition 

 Limestone at Dudley. 



Description. 



In the COLUMNS (Pi. n. fig. 1. to 22.) which I consider as belonging to the 

 animals of this genus, I have noticed two different modes of organization, 

 which inclines me to suspect that although I am only able to treat of one 

 species as decidedly ascertained, yet two distinct species may really exist. 

 Thus, in regard to the surface of adhesion, some columnar joints display 

 numerous radiating striae proceeding immediately from the alimentary canal 

 to the circumference ; (fig 6. to 10.) 'other joints (fig. 1 . to 5.) have only a 

 narrow striated rim with a smooth central area ; and again some columns (fig. 

 11. to 15.) are formed of joints of uniform thickness, from some of which, 

 occasionally, several side arms proceed ; whilst other columns particu- 

 larly those from Mitchel Dean, (fig 17. to 22.) are formed of joints alternately 

 thicker and thinner, smaller and larger, much contracted at their margin of 

 mutual adhesion. In these every second or fourth joint is considerably thicker, 

 showing at its circumference five or six tubercles, which render it angular 

 and its surface waved, to which the joints above and below conjprm. The 

 alimentary canal in both the columns thus distinguished is pentapetalous, 

 a form which I have only noticed in Cyathocrinites rugosus, and in the upper 

 portion of the column of Platycrinites quinquangularis, and some of those 

 genera where the pelvis is formed of five pieces. The form of this pentapeta- 

 lous passage varies in different specimens from the angles being more or less 

 contracted, which renders it more or less conspicuous, and thereby proves the 

 muscularity in this place. 



The AUXILIARY SIDE ARMS. (Pi,, n. fig. 11. to 15.) The tubercles ob- 

 served on some of the columnar joints may be traced on the suite of specimens 

 in my possession through various stages of increase, till at length they form 

 auxiliary side arms composed of numerous joints, articulating by radiating 

 strias, and perforated in the centre by a nourishing vessel which near the column. 



