74 ON THE ECHINODERMATA OF THE 



is to be found in different specimens in this lower angle ; and when very obtuse a much 

 smaller relative proportion of the length of the plate lies below a horizontal line drawn 

 through the lateral angles, than is the case when the proximal angle is smaller. 



The first brachial joint is short and cuneiform ; the second often as long as, or even 

 longer than, broad ; the proximal margin forming a fairly acute angle in the profile 

 contour of the plate. This joint has also the appearance of being very considerably 

 twisted round to the front ; so that the afore-mentioned proximal angle is found opposite 

 the middle part of the margin of the horizontal suture of the first brachial, when seen 

 from the front. The third brachial is a comparatively short joint, of nearly equal 

 length at either side, and bears the first syzygy. The succeeding joints of the ray have 

 their longer side shorter than their breadth, and taper wedge-form to the other side, 

 their profile, when seen from the exact median line of the ray, being regularly triangular. 

 On the lower portion of the ray, the angle formed by the longer side of the arm-joints 

 and the proximal suture is prolonged into a prominent peak, which is also brought 

 somewhat forwards. The neighbouring joint has a little corresponding projection or 

 lip, upon which this articulates ; and owing to this structure, a semitubercular or knobby 

 character is given to the lower portion of the ray, which is highly characteristic of the 

 present species. The rays are very robust, and maintain this character throughout. 

 Towards the extremities the joints become very short, and their breadth equal to 

 several times the length of their longer side. Syzygies occur on the 3rd, 8th, 12th, 

 15th, 18th brachial joint, and so on the first two being very constant, the third some- 

 times varying onto the llth or 13th joint; in the latter case the next syzygy does 

 not occur till the 18th brachial is reached. 



The pinnules are very robust, 100 being present on the one side of an arm of a 

 moderate-sized specimen ; and the joints are more or less compressed. The first five or 

 six upon the ray have the flattened dorsal prominences which give the peculiar saw-like 

 character mentioned by Miiller and others. As a rule, the lowest pinnules in this species 

 are of fairly uniform length, increasing slightly as they proceed along the ray ; some- 

 times, however, the first pinnule is somewhat longer than its immediate successors ; 

 but there is no great disparity in the second and third, such as occurs in the two next 

 species. 



In a first pinnule, measuring 20 millims., were 45 joints ; in another, a fraction 

 longer, 48 joints ; and the third and fifth pinnules measured, within a fraction, the same 

 length. A pinnule taken midway along the ray was 25 millims., and had 36 joints in 

 this position the joints being relatively longer and more cylindrical, and their distal 

 margin finely denticulate. In all the pinnules after the first eight or ten, the two 

 lowest joints are very much larger than the rest, and they maintain this disparity 

 throughout the ray ; their form, also, is noteworthy, the first or articulatory joint being 

 very compressed and somewhat halfmoon-shaped, whilst the proximal margin of the 

 second joint is also considerably incurved, so that a large vacant space is left between 

 the two joints, which is occupied by muscle or ligament, these first two joints being 

 the only ones that preserve along the ray the slightest trace of the dorsal carina?, 

 which have been mentioned above as characteristic of the joints of the entire 



