204 PROCEEDINGS OF THE ACADEMY OF [1886. 



single one in the anterior one. The articular line between the 

 lateral radials and brachials is widely gaping, the union between 

 the two succeeding plates apparently b}- syzygy. They are closely 

 fitted together in the specimens, and a suture is rarely discern- 

 ible. The lower one is short and quadrangular, the upper one 

 axillary. The brachial of the anterior ray is generally twice as 

 wide as high, and truncate at its upper side. 



It has been stated that in the lateral rays the first brachials 

 are placed obliquely against the radials, in consequence of which 

 these two rays lean over toward the posterior side. By this 

 peculiar structure, the outer sloping faces of the bifurcating 

 brachials are brought into a vertical, the inner ones into a hori- 

 zontal position. The vertical side supports laterally another 

 axillar}^ the horizontal side vertically a free arm. The former is 

 followed again by an axillary on one side, and an arm on the other, 

 and so on in the same manner to the last bifurcation, the axillary 

 plates all arranged in a nearly horizontal line, the free arms hav- 

 ing an upright direction. In species with but few bifurcations 

 the position of the brachials is more erect. 



The arms are composed of single joints, which are generally as 

 long as wide ; rounded exteriorly and provided with a deep tri- 

 angular groove at the ventral side ; they are comparatively long, 

 rather stout at the base, but taper gradually upwards. The 

 lateral arms, after their first bifurcation, do not branch again, but 

 give ofi" from every third or fourth joint a large arm-like pinnule, 

 which extends to the end of the arm. The lower pinnule is less 

 than half the size of the arm at the place of attachment ; the one 

 or two succeeding ones have nearly the same size as the arras at 

 the place of their origin. The pinnule-bearing joints appear to 

 be somewhat stouter owing to a thick callosity at their upper end, 

 and their line of articulation is directed obliquely. The interme- 

 diate joints have parallel sides, which show neither fossae nor 

 radiations, and probably were united simply by suture. The 

 anterior ra}^ has but a single arm, which is given ofi" in an upright 

 direction. It is stouter than the lateral arms, and remains fre- 

 quently simple throughout, but when it branches occasionally, 

 the division takes place near the distal end. 



Anal plates two, resting against the basals and the incurved 

 wings of the lateral radials. Their upper side supports a row of 

 very large and heavy quadrangular plates, which are longitudi- 



I 



