422 



ROBERT TRACY JACKSON ON ECHINI. 



saj^ that the ambulacra imbricate aborally and the interambulacra adorally. The imbrication 

 of plates is shown in text-fig. 248, which figure, reversed from the original orientation, also 

 shows a portion of the lantern somewhat displaced, but extending from what Worthen and 

 Miller consider the dorsal side. Professor Duncan's (1889a, p. 16) statement, that Worthen 

 and Miller may have seen the specimen from within, which would account for the direction of 



imbrication as given, is wide of the mark, 

 because their figure is evidently an ex- 

 ternal view. It is perfectly obvious from 

 their figure that Worthen and Miller ori- 

 ented their specimen incorrectly and that 

 the ambulacra imbricate adorally and the 

 interambulacra aborally as usual in Echini 

 (p. 76). As regards the peculiar protuber- 

 ances, one of which is described as "horn- 

 like " by Worthen and Miller, the}' may 

 well be considered as extreme local distor- 

 tions, and the "horn-like" protuberance 

 even as a foreign adherent body. In its 

 length, lateral position, and structure as 

 shown, it appears to have no relation to 

 anything known in other Echini. Pro- 

 fessor Duncan's (1889a, p. 17) view that 

 these protuberances might be considered as marsupia appears to be quite untenable. 



The test is subspheroidal, about 20 mm. in diameter, as gathered from the published figure. 

 The ambulacra are wide, with ten columns of plates in an area, Worthen and Miller say that 

 this number may be and probably is exceeded in the equatorial zone; the plates, which are 

 rather wide hexagons, bear each a pore-pair. The ambulacral plates imbricate adorallj^ (see 

 above discussion). Interambulacra with five columns of plates which are small, somewhat 

 rounded on the suture lines, but almost rhombic in outline. Only four columns of interam- 

 bulacral plates exist in the enlarged fragment (text-fig. 249). The interambulacral plates 

 inil)ricate aborally (see above discussion). The surface of the plates as described is covered 

 with small granules for the attachment of spines. Jaws are present. They are shown poorly 

 in text-fig. 248, and better in Worthen and Miller's Plate 31, figs. 6, 7, the latter figure being 

 doubtfully referred to this species by the authors. 



Chester Limestone, Lower Carboniferous, Prairie du Long Creek, Monroe City, Illinois; 

 same horizon, Pope County, Illinois. Worthen and Miller list the original specimen or speci- 

 mens as in the Ilhnois State Collection, no. 2,481, 



Text-figs. 2-18-2.50. — Lejiuleslhcs tsjHclabilis (Worthen and 

 Miller). Chester Limestone, Lower Carboniferous, Prairie du 

 Long Creek, Monroe County, Illinois; cotype (after Worthen 

 and Miller, 1883, Plate 31, figs. .5a, 5b, 5c). 



24S. Whole test, distorted, a horn-like protuberance extends 

 from one side, lantern protruding; the orientation is reversed 

 from that given by Worthen and Miller. Natural size. 



249. Fragment of test, enlarged X 2. 



250. Horn-like protuberanee, magnified. 



