DESCRIPTIONS OF THE SPECIES. 215 



interradial pieces; while Hall ' said, "A narrow intercalated plate on the anal Bide 

 reaches from the aperture to the radial plate, dividing the interradial on that side into 

 two narrow curving plates." Or, in the still clearer words of Meek and Worthen : — 

 " We find the area between two of the pseudo-ambulacra on the anal side wider, and 

 often more prominent above than the other interamhulaeral spaces, and occupied bv 

 three large elongated pieces, the middle one of which, the anal piece, is lanceolate in 

 form, and with the two interradials tills all the large anal ana down to the base."- 



We are inclined to believe that this is really the case, as do Montgomery 3 and 

 Harris 4 , the latest writers on the subject. Dr. J. G. Hinde has favoured us with 

 the loan of a specimen of E. Canadensis, Montg., in which the sutures of this complex 

 plate (PL XVIII. tig. 1 ( J) are beautifully shown. The sides of the anus are excavated 

 out of the lateral portions of the anal deltoid, and the distal margin out of the central 

 plate. The latter appears to overlap the two side pieces, and to lie on them to a certain 

 extent. Lyon's description of the tripartite structure of the interradii has thus proved 

 to be correct for that of the anal side ; though what we now know to be the parts of 

 the divided anal deltoid were regarded by him as belonging to the ambulacra. 



The summit-plates are often arranged with a singular regularity, which is much 

 more apparent than is usually the case in other Blastoids. Roemer figured seven in 

 E. Verneuili, one in the centre and six peripheral. These were also mentioned by 

 Lyon, together with fifteen others, the nature of which is by no means clear from his 

 description of them. According to Hall the summit is occupied by five or more 

 plates, while one of our own specimens of E. Verneuili shows a central one imme- 

 diately surrounded by seven others, with smaller ones outside them (PI, XVIII. 

 fig. 16). These summit-plates appear to be larger and less numerous in Elceacri/tus 

 than they often are in Schizoblastus (PI. HI. fig. 3) or in Orophocrinus (PI. XV. 

 fig. 12), and are therefore of considerable morphological importance, as we have 

 explained on pp. 73-75. 



We are able to confirm Billings's account of the two hydrospires on each side of 

 the ambulacra of E. Verneuili (PI. XVII. fig. 19), and have also been able to make 

 out the water-vascular ring with the radial trunks proceeding from it (PI. XIX. fig. 7), 

 just as in Pentremites (PL XII. figs. 10, 17). 



Species^. Want of material prevents us giving a critical list of species, but the 

 following have been described under one or other of the three names which have 

 been bestowed on this generic type : — 



1 Fifteenth Ann. Eep. New York State Cab. Nat. Hist. 180:!, p. 146. 



2 Iteport Geol. Survey Illinois, 1866, vol. ii. p. 275. 



3 Canadian Nat. & Geol. 1881, vol. x. no. 2, p. 82. 



4 Iteport Geol. Survey Illinois, 1883, vol. vii. p. 858. 



5 We omit from this list the Elaacrimu Kirkwoodmsis, Shumard, formerly included by us. 



