88 



THE BLASTOIDEA 



upper part ; at the aboral end of the ambulacrum the floor of the radial 



sinus comes below the lancet-plate (cf. Tricoelocrinus). 



Nucleocrimts, Conrad (1842, 

 synn. Elaeacrinus, Roemer, 1851; 

 and Olivanitet, Troost, MS., 

 1849), Devonian, North America, 

 differs much from the genera 

 hitherto described (Fig. X.). Al- 

 though the theca is lofty (often 

 olive - shaped) the BB and RR 

 reach a very short way up it ; 

 the BB and lower part of RR 

 are pressed inwards, and the 

 radial sinus receives only the 

 distal extremity of the ambula- 

 crum. The greater part of each 

 ambulacrum lies between certain 

 int?rradial plates. The posterior 

 interradius contains three such 

 plates a median plate, at the 

 oral end of which lies the anus, 

 and a plate on either side. These 

 lateral pieces meet at their oral 



Eleutlwrocrinus Cassedayi ; oral view x diam. 

 The abnormal, 1. post, radius turned to the 

 observer; r. post, ray has covering-plates (c.p) 

 which in life would have covered over the oral 

 centre; in r. ant. ray the c.p are removed 

 and one sees the whole of the side-plates (s.p) ; 

 these again are removed from ant. ray, exposing 



the lancet-plate (/,) ; removal of 7, in 1. ant. ray 

 shows the hydrospires (A.s). (Based on Shumard 

 & Yandell, and Whiteaves.) 



ends, enclosing the anus, and 

 stretch down between the central 

 piece and the ambulacra. The 



central interradial is smooth, with a median vertical ridge ; but the lateral 

 pieces are transversely grooved, each groove corresponding to a pore 



Fio. X. 



Nucleocrinus VtrneMill. 1, from anterior radius, x J. 2, oral view, show-ins large cover- 

 ing-plates over the peristome (from Brit. Mus. 120), x |. 3, from posterior interradius, x j}. 

 At, anus ; cp, covering-plates, which were continuous over the food-groove (/</) ; IK, iiiterradiii) 

 pieces ; R, radials ; gp, spiracles ; A, deltoids, the limbs of which flank the ambulacra. 



in the ambulacrum. As regards the structure of the other inter- 

 ambulacra there is a difference of opinion. Each contains a lanceo- 



