THE CRINOID HYPOCRINUS. 



901 



■ Stem-facet (PI. XO. fig. 4) cii-cular, mavkeclly concave, bounded 

 by a slight rounded rim ; external diameter 27 mm. ; internal 

 diameter 1-75 mm. Lumen circular, about -3 mm. diameter. 

 There are exceedingly faint traces of about 15 or 16 radiating 

 grooves. 



Infrabasals (PI. XC. fig. 4) closely united. The posterior 

 suture is most distinct, chiefly because a' crack is partially co- 

 incident with it. When the specimen reached me the right 

 anterior suture could scarcely be detected, only being indicated 

 by a faint band of lighter colour. Various processes of prepa- 

 ration have now rendered it perfectly visible. The left anterior 

 suture at first seemed conspicuous, but the appearance was due to 

 a rather irregular crack continuous with that noticed along the 

 posterior suture. The left anterior suture itself could not be 

 traced with certainty ; it now appears to be only in part co- 

 incident with the crack. In the concavity of the base, after 

 careful preparation, there are dimly seen two dai'k streaks 

 running from the lumen in the direction of the posterior and 

 right anterior sutures respectively. There appears to be a third 

 such streak a little on the anterior side of the above-mentioned 

 crack ; and this streak probably indicates the position of the left 

 anterior suture. 



It follows from the preceding account that Beyrich's description 

 and figures of the base, as composed of two large plates and one 

 small plate, though unsupported by valid evidence, were in the 

 main correct. His figures are little more than inexact diagrams, 

 and neither they nor the text indicate the position of the small 

 infrabasal ; it is anterior (text-fig. 158). 



Text-fig. 158. 



RR 



BB 



IBB 



Sypocrinus scJineideri. 



Analysis of the cup of the holotype. 



The pei'iproctal outline is dotted in. Nat. size. 



Heights of IBB : — anterior 8'7 mm. ; right large IB 7'3 mm. 

 along median line, 9'3 to posterior angle ; length of posterior 

 suture 7"3 mm. 



Basals bounded by fairly distinct sutures, emphasized by the 



