64 CANADIAN FOSSILS. 



The principal difference between this genus and such genera as 

 Dendrocrinus, Pcrocrinus, Palaocrinus, and Cyathocrinus, consists in 

 the incompleteness or rudimentary character of its plates. The 

 arrangement of the parts of the skeleton is the same. 



Reteocrinus stellaris, Billings. 

 Plate IX. Figures 4a-4e. 



Description. — The cup of this species appears to be about five 

 lines in height and six lines in width. The projecting processes of 

 the plates, and also the joints of the arms to first bifurcation, are 

 rounded on the outside, and half a line in thickness. The first joint 

 of the right anterior ray (which is the first primary radial,) has three 

 processes, the upper one of which supports an arm, while the two 

 lower rest, one of them on one of the upper processes of the azygos 

 sub-radial and the other upon a process of the right anterior sub- 

 radial. It is probable that the other rays are constructed and 

 situated in nearly the same manner. The azygos sub-radial has five 

 processes, three above and two below. The central of the three 

 upper processes supports an upright series of joints (as represented 

 in figure 4a, plate 9). If this series of joints constitute a true arm, 

 then there must be six arms in this species. The right arm divides 

 above the fourth joint; I have not seen the other arms distinctly. 

 The spaces between the arms are occupied by numerous small 

 stellate plates, which may have belonged either to an integument 

 connecting the arms, or to the covering of the abdomen. The 

 column is round, and composed of very thin plates near the base of 

 the cup. At the distance of about one inch and a half below the 

 base of the cup the joints alternate in thickness. 



None of the specimens collected are perfect, and the characters of 

 the species therefore have not been fully ascertained. 



Explanation of Figures. Plate IX. 



Figure 4a. View of the anterior side of a specimen. 



" 46. A specimen retaining a piece of the column ; 4c, several of the joints 

 enlarged. They appear to be nearly equal in size, and sharp-edged 

 at the base of the cup. 

 " id, 4e. Fragments of this species. 

 [In 4a and 4e the small stellate plates between the arms are represented.] 



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



