474 PEOF. p. M. DUNCAN ON SOMB 



resembling those of the radial shields ; and there are spines and 

 spinules, in some sjDeeimens, near the centre. 



Towards and on the interbrachial spaces, reaching in a trian- 

 gular patch on to the under surface, are spinules, which become 

 crowded inferiorly. They are slender, with swollen bases of attach- 

 ment, and have long trifid thorns. 



There is a reddish tint on the centre and in the interradial 

 spaces, and it also sometimes encircles the whole disk as with a 

 narrow band. The tips of the stumps and spinules are often red. 

 The disk is covered with skin, under which traces of scales may 

 sometimes be seen ; and below the disk is naked beyond the patch 

 of spinules. 



Inferiorly, the disk-membrane joins on by two plates to the 

 distal joint of each mouth-shield: the generative slits are large, 

 and the generative plates are broad and large and very visible at 

 the side of and above the arms. 



The mouth-shields are small, broader than long, diamond-shaped, 

 rounded at the sides, angular within and curved without, where 

 there is union with the edges of the generative slit. The oral 

 edges are slightly re-enteringly curved. The madreporic shield is 

 elliptical and the largest. 



The side mouth-shields are rather large ; they are narrow at 

 their inner edge where they do not unite, and they are broad and 

 triangular where they are in contact with the first lower arm-plate. 

 Their oral edge is curved, with the concavity towards the jaws. 



The pairs of jaws are slender and arewidely separate, and each 

 jaw of the separate angle is distinct near the mouth-shield. 



The tooth-papilla3 are in a very long narrow oval ; they are 

 small, and crowded in a row of six or more inferiorly, and be- 

 come gradually larger above until they approach the true teeth. 

 "Within the edge of the oval thus formed there is a well separated 

 mass of tooth-papillse in two rows, and they are larger than those 

 around. The number of papillge is variable. 



The teeth are narrow, flat, slightly rounded, and sometimes 

 have a boss on the free end ; they increase in size upwards, but 

 the highest is sometimes smaller than the others. There are five 

 in all. 



The lower arm-plates increase in size from the oral ring to 

 where the arm is well free from the disk, and they retain a con- 

 siderable dimension until the terminal thii'd, where they decrease 

 gradually. Their typical form is slightly broader than long, 



