24 CANADIAN FOSSILS. 



known, of an uniform size, there being on an average about ten in 

 the length of two lines. 



This species so closely resembles H, tumidus of the Trenton lime- 

 stone, that I have had much doubt as to the propriety of separating 

 it therefrom. The only differences that I can perceive are, that it is 

 always smaller than the Trenton form, the plates more coarsely 

 granulated under the lens, and not so convex in their centres. 

 The column does not taper so rapidly, and it is composed of joints 

 which are thicker in proportion. In a well-preserved specimen of 

 H. tumidus the column exhibits from eight to ten joints in the length 

 of one line, whereas in H. pristinus there are only five. Under these 

 circumstances I have thought it best to distinguish the Chazy speci- 

 mens by a separate name for the present. 



Locality and formatio7i. — Detached plates are rather common in the 

 Chazy limestone at Caughnawaga, and at various localities on the 

 Islands of Montreal, Jesus and Bizard ; also in the front part of the 

 Township of Hawkesbury. Perfect specimens are rare. 



Genus PALiEOCRiNUS, Billings. 



FORMDLA : 



Basal plates, 5. 

 Sub-radial plates, 5. 

 Radial plates, 1x5. 



Azygos inter-radials, 1-3. 

 Regular inter-radials, 0. 

 Calycinal ambulacra, 5. 



Figure 10. 



Figure 10. Diagram of the cup of the genus Paleocrinus. The azygos inter-radial 

 space is left blank in the figure, as it is not certain how many plates it contains. 



Generic characters. — Cup, oval or pyriform, composed of five pen- 

 tagonal basal plates, alternating above which are four hexagonal and 

 one heptagonal sub-radial plates, and above these five radials bearing 

 the free arms. The heptagonal sub-radial supports upon its trun- 

 cated summit one, two, or three small azygos inter-radials. The rays 

 are slender, and free from the second joint inclusive. There are five 

 calycinal ambulacral grooves radiating from the centre of the abdo- 

 minal suiface to the bases of the arras, where there appear to be 



