CHAP. ix.J THE DEEP-SEA FAUNA. 439 



intermediate joints is complete. At the top of the 

 stem five little calcareous lumps like buttons stand 

 out from the projecting ridges, and upon these and 

 upon the upper part of the stem the cup which 

 holds the viscera of the animal is placed. These 

 buttons are of but little moment in this form, but 

 they represent joints which are often developed into 

 large, highly-ornamented plates in the various tribes 

 of its fossil ancestors. They are called the ' basal ' 

 plates of the cup. Next, in an upper tier, alternating 

 with the last, we have a row of five oblong plates 

 opposite the grooves of the stem, and all cemented 

 into a ring. These plates are separate when the 

 animal is young ; they are called the ' first radial ' 

 plates. They are the first of long chains of joints 

 which are continued to the ends of the arms. Imme- 

 diately above these plates, and resting upon them, 

 there is a second row of plates nearly of the same 

 size and shape, only they remain separate from one 

 another, never uniting into a ring. These are the 

 ' second radials,' and immediately upon these rest 

 a third series of five, very like the plates of the 

 other two rows, only their upper surfaces rise into 

 a cross ridge in the centre, and they have the 

 two sides bevelled off like the eaves of a gable, to 

 admit of two joints being seated upon each of them 

 instead of one. This last ring of joints are the 

 ' radial axillaries,' and above these we have the first 

 bifurcation of the arms. These three rings of 

 radial joints form the true cup. In the modern 

 species they are very small, but in many fossils 

 they acquire a large size, and enclose, frequently 

 with the aid of various rows of intermediate or 



