115 



Fig. 76. 



a 



6^ 



Fig. 73 Apex'of Nucleocrinus Verneuilii Troost. ambulacral groove ; pore through 

 which groove enters into the interior ; one of the ten spiracles ; mi\ oro-anal apeiture. 

 74 Anterior side of a specimen ; the anterior interradial. 75 Apex of a specimen which 

 has lost the integument that covered the centre. 76 Diagram of the plates of the test ; 

 r/, ambulacral plates; 6, the basals ; c, plates of the apex; one of the interradials ; /, 

 forked plate. 



The body of this remakable genus is ovate, elliptical or oblong, and 

 inclosed in a shell of strong perisomatic plates, which are, in general, so 

 closely anchyclosed that the sutures between them cannot be distinguished- 

 According to Mr. Lyon, who, through his long continued geological 

 researches, has collected and studied a vast number of specimens, there are 

 three minute, lozenge-shaped, or quadrilateral basal plates, situated at the 

 bottom of the columnar pit, always concealed when the column is present. 

 These are surrounded by three other plates, the six altogether correspond- 

 ing to the six pieces which constitute the compound basal plates of JPen- 

 tremites. They are represented at fig. b, as figured by Mr. Lyon (Geol. 

 Ky., vol. iii, pi. v, fig 1, h.) 



-H^In the next series there are five plates which are undoubtedly the hom- 

 ologues of the five forked plates of Pentremites. They are very short 

 and confined to the base of the body. They form a shallow basin with ten 

 re-entering angles in its margin. Fig. 76 /. 



Alternating above the forked plates, are five pieces corresponding to the 

 deltoid or interradial plates of Pentremiies. Some of these are lanceolate 

 inform (fig. 76 c?), their broader extremities fitting into the angles between 

 the forked plates. They taper to a point upward, and their sides are 

 bevelled so as to pass under the ambulacral plates, to which they are, in 

 general, so closely united, that the line of junction is indicated only by 

 the difference in the markings of the surface. Owing to this structure, 

 these plates have not always been recognized by the authors who have des- 

 cribed this genus. They were first pointed out by Mr. Lyon. The fifth 

 deltoid or interradial plate is truncated at its apex for the reception of the 



