CANADIAN FOSSILS. 69 



margins of the plates and extend towards the centre, but do not 

 open out on the exterior surface. On the interior surface they open 

 between the edges of the plates. Column, arms and orifices unknown. 

 Greneric name from palaios, ancient. 



The most abundant species of this genus appears to be identical 

 with that fossil of the Chazy limestone to which Professor Hall has 

 given the name of Actinocrinus tenuiradiatus. (See Palaeontology of 

 New York, vol. i. p. 18, plate iv. figs. 8 and 9.) I have ascertained 

 however that it is a Cystidean. No perfect specimens have been 

 found, but several fragments, which 1 have collected, consisting each 

 of about one-third of the body, shew that it is a genus allied to 

 Comarocystites, Sphceronites and others of the many-plated group. 



This genus appears to be closely related to Amygdahcystites. 



XVI. Pal^ocystites tenuieadiatus. Hall sp. 



(Actinocrinus tenuiradiatus, Hall. Pal. N. Y., vol. 1, p. 18, pi. iv, figs. 8 and 9.) 

 1 



IWilTifiTO 



Fig. 1. View of exterior of several plates of P. tenuiradiatus. 

 Fig. 2. Edge of a plate, shewing the entrances of the pores. 

 Fig. 3. Inside of several plates, shewing the opening of the 

 pores in the suture. 



Description. — Large specimens are two inches or more in length 

 and pyriform in shape, the upper part of the body being the largest. 

 The plates are depressed conical, and when a little worn are all 

 covered with deep fissure-like striee, which are at right angles to 

 the edges. These striae cross from one plate to the next contiguous, 

 so that one half is upon one plate and the other half upon another. 

 At the suture in the bottom of each of those fissures is a small 

 aperture that penetrates through, being partly excavated in the 

 margins of each of the plates respectively. The eflfect of this mode 

 of striation is to cover the whole surface of the fossil with small 

 rhomboidal areas, each of which occupies portions of two plates. 

 There are as many half-areas on each plate as the plate has sides. 

 When the surface has not been worn the interesting fact may be clearly 



