1908 548 F. A. Bather— Studies in Edrioasteroidea. 



" In all the specimens . . . the rays curve round to the right 

 hand." As the figures show, this means sinistrally or contra-solar, as 

 is actually the case in Bigsby's specimen. 



"The marginal plates of the rays do not appear to alternate 

 regularly." They do alternate, however, and the contrary appearance 

 is due to the irregularities of the covering-plates. 



" There are two rows of small circular indentations on each side of 

 the rays, corresponding in their position to the ambulacra! pores of 

 E. Bigsbyi, only that in the latter they are in the bottoms of the 

 grooves." I only see one row of 'indentations,' but the appearance 

 of another row is occasionally produced on the extreme edge of the 

 ray by the rounding of the ends of the flooring-plates. The structure 

 of the anterior ray in our specimen leaves me in no doubt that the 

 indentations were actual pores, corresponding to the pores of E. Bigslyi, 

 which had only one row of pores, not two, as Billings supposed. 1 The 

 difference between the two forms really is that here the pores are well 

 outside the covering-plates, whereas in Edrioaster they were roofed in 

 by them, a fact not known to Billings. 



Bemarks on other Specimens referred to A. Dicksoxi. 



The specimen formerly belonging to Dr. James Grant has already 

 been mentioned. Since the present paper was first written, Dr. J. M. 

 Clarke, in a valuable article entitled "New Agelacrinites " (Bull. 

 N.Y. State Mus., vol. xlix, pp. 182-98, pi. x, December, 1901), has 

 published a diagram based on Grant's figure (p. 190, fig. 3), and 

 from his legend it appears that the diameter of the specimen is only 

 21*5 mm., and not 48 mm. as it appears in the original drawing. 

 These illustrations indicate some resemblance to Bigsby's specimen, 

 but the small adorally imbricating plates seen on the margin in the 

 right anterior interradius do not appear in harmony with the adjoining 

 plates of the periphery, which are all large, just as they are in 

 Bigsby's specimen. At all events, such a figure, unsubstantiated 

 by any description, cannot be held to prove the existence of the 

 imbricate border characterising Agelacrinus, Lepidodiscus, and a few 

 other genera. 



A distinct imbricate border of Agelacrinus-tyipe is shown in pi. ii, 

 fig. 2, of Professor Otto Jaekel' s "Stammesgeschichte der Pelmatozoen" 

 (Merlin, 1899). The specimen, which is in the collection of Professor 

 Freeh at Breslau, and comes from the Trenton Limestone of Ottawa, 

 is assigned by Dr. Jaekel to A. Dicksoni. On p. 50 he says of this 

 species: " Thecalplatten zwischen den Ambulacren besonders gross, 

 Ambulacra ziemlich kurz gedreht, Saumplattchen stark skulpturirt." 

 The word ' Saumplattchen ' is usually translated by ' covering-plates ' 

 or ' ambulacrals,' and in the explanation to pi. ii Dr. Jaekel applies 

 the word ' Ambulacralia ' to two of the plates that in his opinion 

 cover the subvective groove. These are strongly pitted on the sides 



1 See the diagrams and brief account of Edrioaster Bxgabyi in "A Treatise on 

 Zoology," ed. E. Ray Lankester, vol. iii, Echinoderma, p. 209. Also F. A. Bather, 

 "What is an Echinoderm?" 1901, and Encycl. Brit. Suppl., Art. Echinodermata, 

 1902. 



