164 Dr. G. J. Hiude on a 



Radials. — The first or true radials are relatively large 

 flattened plates, spade-shaped or trapezoidal in form, varying 

 from 10 to 12 millim. in height, 8 to 11 millim. in width at 

 their bases, and between 10 and 14 millim. at their summit- 

 margins. They are about "75 millim. in thickness, but in 

 the central upper portion increase to 2 millim. The basal 

 and the two lateral margins are straight, whilst the distal is 

 in some cases straight and in others is slightly elevated 

 toAvards the centre, where there is a shallow semicircular 

 excavation with radial ridges and grooves for the reception of 

 the second radial. The sutural surfaces of the first radials, 

 by which they connect with each other and the basals, are 

 covered with very delicate transverse ridges and grooves (PL 

 VI. fig. 5), whilst those of their distal margins, which connect 

 with the interbrachial plates, run in a longitudinal direction 

 (PI. VI. fig. 4). 



The second and third so-called radials are short thick plates 

 or joints, whose united length varies from 2*5 to 3*25 millim., 

 and they are about 3*5 millim. in width. The lower and 

 shorter of the two has an oblong or trapezoidal outline, and 

 varies in different specimens from "8 to 1*25 millim. in height, 

 whilst the third or axillary* radial is a small pentagonal 

 joint 1*7 to 2 millim. in height. There are one or two spines 

 on the dorsal surfaces of each of these upper radials. Laterally 

 the upper radials are united by sutures to the interbrachial 

 plates. 



Arms and Pinnules. — The two sloping upper facets of the 

 axillary radial each support a single arm. The first four 

 joints of each arm are subequal, with four unequal sides, and 

 approximately semielliptical in transverse section. They are 

 disposed in a single vertical series, and their united length is 

 3*2 millim. The sutural facets of these joints are strongly 

 grooved radially. The inner lateral faces of the first two 

 joints of each arm are bevelled and grooved and suturally 

 connected with the corresponding arm-joints springing from 

 the adjoining axillary facet. The next two joints in each arm 

 diverge from those of the corresponding arm ; but they are 

 nevertheless united together by an elongate tongue-shaped 

 interaxillary plate. Above the fourth joint in each arm the 

 joints become wedge-shaped and form a double alternate 

 vertical series. The inner edges of these joints are dove- 

 tailed into each other, so that the sutures form a zigzag line 



* Au abnormality occurs in one of the radial series of one of the speci- 

 mens, which has two joints or plates between the first radial and the 

 axillary, thus exhibiting four radials altogether. 



