LOWER HELDERBERG ROCKS. lOS 



Mailacriims iiobilissimus ( n. s.)- 



Plate II. Fig. 1-4; and Plate II A. Fia. 1. 



Body large, obconical below, becoming obtusely pentagonal above by the 

 prominence at the base of the arms. Plates with obscure radiating 

 ridges, which become conspicuous near the sutures. Surface finely 

 granulose. Basal plates four, wider than long; three pentagonal, and 

 one hexagonal and truncated above ; the hexagonal basal plate anterior. 

 First radial plates about as long as wide ; four heptagonal, the anterior 

 one hexagonal. Second radial plates sometimes longer than wide ; four 

 heptagonal and one hexagonal. Third radial plates about as wide as 

 long ; four heptagonal (?) and one octagonal. Intermediate plates large ; 

 four on each side of the four regular sides. Anal plates, or^ interradial 

 plates upon the anal or irregular side, nine. Brachial plates two resting 

 on each third radial, and each of these succeeded by two others which 

 rest successively upon each other, with an intercalated single range of 

 three or four small plates between. The third brachial plate on each 

 side supports upon its upper edge a double set of plates, the outer ones 

 of which on each side support the auxiliary arms, while the inner ones 

 support the plates forming the centre or principal arm in direct suc- 

 cession, and its subordinate branches. 



Arms composed of double series of alternating plates, which are broader 

 than long, slightly interlocking at their inner margins, producing a 

 slight groove along the centre of the arm. Every fourth or fifth plate 

 on each side becomes thickened on its outer margin, and obliquely 

 truncated, giving origin to the lateral branches or armlets. The entire 

 arm thus consists of its own articulations proper, and supports a series 

 of lateral branches to the number of more than thirty on each side. 

 The armlets or fingers are gradually tapering, nearly round, and com- 

 posed of double series of alternating plates much broader than long, 

 and closely interlocking at their wedgeshaped inner margins. Each one 

 of these plates supports a tentacle on its outer margin, giving a double 



[ PAL^ONTOLOar III.] 14 



