ICHTHYOCRINIDAE 315 



tends occasionally to obscure the clearness of this distinction, the anal series appearing nearly 

 to fill the area with little appearance of bordering integument ; these cases, however, are 

 evidently sporadic variations in one abundant species. 



As in Ichthyocrinus, there is in this genus considerable degeneration of the base, with a 

 tendency to resorption of the infrabasals. In the type specimen of E. concavus they have 

 almost disappeared externally (PL XL, fig. 40-), but a small portion at the left side is visible 

 in the interior (fig 4b) ; and in the type of E. rofei (fig. jb) about one-half of the infrabasals, 

 including the entire right posterior small plate, have been resorbed. This condition of the 

 type of E. concavus gave rise at one time to the impression that the genus was monocyclic. 



The literature relating to Euryocrinus is full of confusion, owing partly to the inade- 

 quacy of the original description by Phillips (Geology of Yorkshire, vol. 2, 1836, p. 205). 

 His generic and specific description was as follows : " Pelvis opening pentagonal, arrange- 

 ment of plates like Encrinus; internal cavity very large." This allusion to Encrinus led the 

 Austins, and after them Bronn in his Lethaea Geognostica, 1856, to class it with the 

 Encrinoidea or Encrinidae ; while the appearance of the interbrachial plates shown by 

 Phillips's figures induced Bronn afterwards in his Klassen und Ordungen des Thierreichs, 

 i860, to place it as a synonym under Actinocrinus, in which he was followed by Von Zittel in 

 Handbuch der Palaeontologie, 1879. The fact that the peculiar structure and characters of 

 the Flexibilia were not then understood may account for much of this early misconception of 

 the relations of this form ; for Phillips's figures, although not quite perfect, were good enough 

 to indicate clearly the systematic position of the genus, as was pointed out by Wachsmuth and 

 Springer in 1879 (Rev. Pal., pt. 1, p. 34), who thought it possibly identical with Ichthyocrinus, 

 which at that time was supposed to include species with and without interbrachials. 



In the meantime Rof e 1 figured and described under the type species a specimen from 

 another locality (PI. XL, fig. jb), upon which he based a more detailed description in the 

 terminology of De Koninck, showing two important facts, viz. : ( 1 ) a tripartite base and five 

 " subradials " ; (2) the overlapping of the distal face of the radials and lower brachials by 

 the succeeding plates. These structures he described more accurately than some of his prede- 

 cessors had done, thus indicating clearly the dicyclic base and loose articulation of the Flexi- 

 bilia. Rofe did not make any suggestion as to the systematic place of this form, but from two 

 allusions in his paper to features in which it was thought similar to Actinocrinus, it may be 

 inferred that he considered its affinities to be with that genus. 



In 1888 Bather and Gregory, having before them the types of both Phillips's and Rofe's 

 descriptions, proposed to refer Rofe's specimens to a new species, E. rofei, but their descrip- 

 tion was never published ; and when in 1905 I had the opportunity to examine the type 

 specimens in the British Museum, Dr. Bather very generously placed their notes at my dis- 

 posal, and I have pleasure in publishing the species under their names. In 1906, 2 as a result 

 of the examination of the original material, I indicated the definite position of this form as 

 a valid genus. 



Euryocrinus, so long ignored and misunderstood, and hitherto represented only by the 

 four figured types from the English Lower Carboniferous, proves to have a wide range, 

 both geographic and stratigraphic. It has now been recognized in America by well-defined 

 species both from the Devonian and Carboniferous. The former occurrence is interesting as 

 adding another to the number of Carboniferous genera originating in the Devonian, but the 

 latter is still more so for its importance in relation to the stratigraphy. It has not been found 

 among the prolific faunas of the Keokuk and other later formations, but only in the Knob- 

 stone, near the base of the Lower Carboniferous, at a horizon strictly equivalent to that in 

 which the English species occur. The English specimens have been described under three 



1 Geological Magazine, vol. 10, 1873, p. 263, pi. 11, figs. 11, 11a, b. 



2 Journal of Geology, vol. 14, p. 483. 



