138 PEOF. P. M. DUNCAN ON AN 



On an unusual Form of the Genus Hemipholis, Agass. 

 By Prof. P. M. Maktin Duncan, F.B.S., P.L.S., &c. 



[Read May 6, 1880.] 

 (Plate VI.) 



Amongst some dredgings from off the Agulhas Bank, south-west 

 of the Cape of Good Hope, given to me by Dr. Wallich, I found 

 several small Ophiurans. One of them struck me at once as pre- 

 senting a very unusual combination of structures. The disk was 

 symmetrically plated above, the arms were almost moniliform 

 and had a few spines projecting from their sides, and the oral 

 apparatus, elongated downwards, had its teeth in close apposi- 

 tion. A non-plated skin covered the interbrachial spaces ; and 

 no proper mouth-papillae or tooth-papillae were visible. These 

 characteristics were so suggestive, that a careful examination of 

 the form was necessary. 



The specimen is a dry one and brilliantly white in colour. The 

 disk is slightly pentangular in outline, and it is tumid above, 

 where it is covered with a few large and regularly placed plates 

 united at their edges. 



There is a large central rosette occupying the greater part of 

 the upper surface, and the central plate (a regular pentagon) is 

 the largest. The other five which surround it are slightly smaller, 

 and are united to it and to their neighbours by straight edges. 

 Their external margin is curved, and they are rather unequal in 

 size. 



The radial shields are large, and some are separated, orally, by 

 a minute triangular scale, which is in contact with one of the 

 plates of the rosette; but where this scale does not exist, the 

 radial shields are united together, and are in broad contact with 

 the outer rosette-shields. 



Their distal margin is broad, sharp, and slightly incurved where 

 it arches over the upper surface of the arm. In the interradial 

 spaces there are only two plates, which are large, one being in 

 contact with the rosette and the other extending to the margin of 

 the disk, where it ends in a sharp edge. 



Underneath, the disk is more pentagonal in outline than when 

 seen from above, and the margin is sharp and distinct. There 

 are no plates in the interbrachial spaces ; but there is a skin 

 there, which is covered with a very delicate cellular coat. 



