54 The Ottawa Naturalist. [Aug.-Sept. 



Specimens of this species are rare and the best one known is 

 that figured by Dr. (now Sir James) Grant in the Ottawa Field 

 Naturalist. During my incumbency as Invertebrate Paleonto- 

 logist to the Geological Survey, this specimen was donated, 

 among other valuable fossils, to the Victoria Memorial Museum, 

 and after comparing it with Billings' and Bather's figures, I 

 am convinced that it is a real Agelacrinites dicksoni. Bather 

 states that Lehetodiscus difi^ers from Agelacrinites, first, in the 

 absence of a differentiated margin il zone; this I believe is due 

 to the imperfection of the specimen he studied; second, he 

 regarded it as having a less flattened and less sessile habit ; this 

 also proceeds from the study of an incomplete specimen ; third, 

 "It seems clear that the side plates, here called flooring plates, 

 are homologous with the flooring plates of Edrwaster. Whether 

 those plates have homologues in the Agelacrinidae is a matter 

 for debate ; at any rate, no genus of that family has similar plates 

 with intervening depressions so like pores." I may have mis- 

 understood the figures and descriptions of both writers, but as I 

 understand it, the "flooring plates" of Bather in Lehetodiscus 

 are the same as the "outer covering plates" of Foerste, and 

 Bather's specimen was not so preserved as to enable him to get 

 at the real flooring plates, which in a Canadian specimen, are 

 concave and single, not double. (Compare Dr. Bather's fig. 1, 

 p. 545, with Dr. Foerste's figs. 1, pi. 1, fig. 4, pi. 2, and fig. 4, pi. 

 3, or, for the genus Thesherodiscus, fig. 8, pi. 1). The small 

 plates which Dr. Bather took for the real covering plates are the 

 "median or intercolated covering plates" of Foerste. I see no 

 real difference between the structure of the subvective system 

 of Lehetodiscus and such a typical (Ordovician) Agelacrinites as 

 A. pileus, except in the large pores between the lateral covering 

 plates. These may, however, be of such importance as to justify 

 the restriction of Lehetodiscus to the species L. dicksoni and L. 

 loriformis, and the creation of two new genera for the reception 

 of the other species here described. 



Lebetodiscus dicksoni Billings. 



Billings, Rept. Progress, Geol. Sur. Canada, 1857, p. 294; 

 Can. Org. Rem., dec. 3, 1858, p. 84, pi. 8, figs. 3, 3a, 4, 4a; 

 Chapman, Expos. Min. Geol. Canada, 1864, p. 110; Grant, 

 Trans. Ottawa Field-Nat. Club, 1, No. 2, 1881, fig. 9; Jaekel, 

 Stamm. Pelmat. 1899, p. 50, pi. 2, fig. 2; Clarke, Bui'. N. Y. 

 State Mus. 49, 1901 , p. 191 , fig. 3 ; f^g'd without name by Sowerby , 

 Zool. Journal, 1825, 2, p. 318, pi. 11, fig. 5. 



Of this rare species, the Museum of the Geological Survey 

 contains the type, another poor specimen collected by Billings 

 (No. 1415), a specimen collected by Mr. Fitzpatrick at Peter- 



