88 



THE BLASTOIDEA 



Ks 



Sc- 



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



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



Nudeocrinus, Conrad (1842, 

 synn. Elaeacrinus, Roemer, 1851; 

 and Olivanites, 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 

 interradial plates. The posterior 

 interradius contains three such 

 plates a median plate, at the 



which in life would have covered over the oral oral elld of which lies the anus, 

 centre ; in r. ant. ray the c.p are removed and a plate Oil either Side. These 

 and one sees the whole of the side-plates (s.p) ; , , f f f i ora | 



these again are removed from ant. ray, exposing lateral pie* 

 the lancet-plate (L) ; removal of L in 1. ant. ray 

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

 ' Whit 



Fid. IX. 



Eleutherocrinus Cassedayi ; oral view x 6 diain. 

 The abnormal, 1. post, radius turned to the 

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

 would have covered over the oral 



& 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 



t.e 



R... 



Nucleocrinw Vernetitti. 1, from anterior radius, x f. 2, oral view, showing large cover- 

 ing-plates over the peristome (from Brit. Mus. E20), x $. 3, from posterior interradius, x f . 

 As, anus ; cp, covering-plates, which were continuous over the food-groove (/</) ; IR, interradial 

 pieces ; R, radials ; sp, 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- 



