/ 



64 CANADIAN FOSSILS. 



Each one of the large joints bears a pinnula, and the ambulacral 

 groove is situated not on the top of the arm, but on one side. 

 On the posterior side of the fossil the groove is on the left side of 

 the arm. On the apex there appears to be an interruption, as if 

 one of the joints were absent ; the ambulacral orifice is no doubt 

 situated at this point, but it has not been clearly made out in any 

 of the specimens yet procured. From this supposed position of the 

 ambulacral orifice proceeding forward the groove is on the right 

 side of the arm, the mouth bemg on the left, as shewn in plate vi. 

 fig. la, at m. 



The column is round, smooth, and composed of thin joints. 



In this interesting form we have an example of a Cystidean with 

 a body composed of an indefinite number of plates, like the Sphcero- 

 nites, and with the arms arranged exactly as they are in Pseudocrinites, 

 a genus characterised by a few plates which are definite in number. 



Explanation of Figures. Plate VI. 



Fig. la. The left side of a specimen ; m, the mouth. Fig. \b. Right side of the same. 

 Ic, posterior ; and Id, anterior views. The groove is not clearly shown in 

 this specimen, le, one of the plates enlarged. 



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

 Collector. — E. Billings. 



XII. Amygdalocystites tenuistriatus, Billings. 

 Plate VI. Figs. 2a.-2f. 



(^Canadian Journal, vol. ii. p. 271, 1854; Geol. Survey of Canada, Report, 1856, p. 289.) 



Description. — Body elongate, ovate ; plates smooth in the centre ; 

 a low rounded ridge proceeds from the smooth space in the centre 

 of each plate to each of the angles, where it meets the similar 

 ridges which radiate from the centres of the adjoining plates ; 

 between these ridges the triangular spaces are finely but very 

 distinctly striated at right angles to the sutures. The mouth is 

 close to the arm on the left side, near the summit. 



The specimen represented by figs. 2a and 2h is the one upon 

 which I drew up the original description published in the Canadian 

 Journal in 1854. It shews only fragments of the arm, and the 

 surface of the plates is so different from that of A. jiorealis, that I 

 then had no doubt of the distinctness of the two species. Last 

 summer, however, I found at Belleville, Canada West, the other 

 specimen, fig. 2c, which has much the form of A. jiorealis, and the 



