LOWER HELDERBERG ROCKS. 147 



PLATES OF UNDETERMINED CRINOIDIAN OR CYSTIDIAN BODIES. 



Plate LXXXVIII. Fig. 5-9. 



Tlie specimens are thickened hexagonal or irregular plates, with margins in- 

 dicating a suture-like junction with other plates or some other similar body : they 

 have all a cicatrix upon the centre of the inner side. The surface aspect and texture 

 do not differ from plates of Edriocrinus; but with our present knowledge of that 

 fossil, these could only be referred conjecturally to the summit of the known species, 

 or possibly are the free bases of a similar form. 



ADDENDA. 

 Maiiacrinus raiuosus (n. s.). 



Plate XL Fio. 2 & 3. 



Body urnshaped. Basal or pelvic plates small. Radial plates longer than 



wide. Arm-plates two, resting on the upper sloping edges of the third 



radial, producing a double series, which again bifurcate on the third 



brachial plate above, giving origin to two pairs of arms ; the two inner 



or adjoining arms similar, and the two outer arms similar to each other. 



The central pair of arms bifurcate irregularly at least three times above 



the separation ; each branch above the last bifurcation being composed 



of a double series of wedgeform plates, and below these points of a 



simple series of quadrangular plates. The lateral arms remain simple. 



Tentacula round, apparently furnished with a second series of tentacles. 



Surface of plates marked by strong radiating ridges. 



This species presents another modification of the arm structure, intermediate to 

 that of JVf. nohilissimus and that of M. plumosus. The lateral arms of each double 

 pair, or those proceeding from each radial series, represent the auxiliary arms of 

 M. nobilissimus, M. pachydactylus, etc., while the central pair represent the large 

 or principal arm of that species; the bifurcations being analogous to the armlets of 

 those species. The modifications of structure aflect only the arms : the body and 

 base of arms are composed as in those species. 



Fig. 2. The specimen, natural size. 



Fig. 3. Diagram of structure, showing relations of radial series to arms, etc. 



Geological position and locality. Same as M. nobilissimus. 



