42 CANADIAN FOSSILS. 



margin where the arms become free, than it is at the bottom ; the 

 basal plates are low and broad, the sub-radials double the height of 

 the basals and the arm-bearing plates rather more than two thirds 

 the length of these latter ; the arms half the breadth of the plates on 

 which they stand, and broadly rounded on the back ; they all divide 

 at the height of about three lines, and again at the same distance 

 above ; there are three or four joints in each of the undivided por- 

 tions. The ray on the left-hand side of the base of the proboscis, 

 which in the generic description is said to have two of its plates 

 included in the cup, in this species has the second plate free, with 

 the exception that it is united on one side to the plates of the 

 proboscis ; it is however nearly as broad as the first radial plate upon 

 which it stands, and one-third wider than the first free joint of the 

 arm which rests upon it. This character connects Dendrocrinus with 

 Cyathocriniis, in which the second joint of the ray in question is 

 entirely free. The column as before mentioned is circular, broad at 

 the base of the cup, and rapidly diminishing in size for a short 

 distance below ; it is in this part smooth, but farther down enlarges 

 again, and is composed of thick round-edged compressed spheroidal 

 joints very similar to those of Heterocrinus Canadensis. In one perfect 

 specimen the height of the cup is three lines, the diameter of base 

 two lines and a half, and at the margin three lines and a half; length 

 of the arms to first division three lines and a-half, to second division 

 six lines; width of arm to second free joint one line, and of the 

 proboscis the same. In another individual this organ is wider than 

 the arm ; in a third specimen the arms divide at the fifth joint, but 

 in every other respect it is the same as this species, although slightly 

 more slender. 



Explanation op Figuebs. Plate IV. 



Figure la. Anterior side. 



" \h. Column, a little enlarged. 



" 2a. Side view of a specimen. 



" 2h. Column of same, enlarged. 



Locality and formation. — Trenton limestone, City of Ottawa. 



