74 PEOF. P. M. DUNCAN ON A 



spinules on, the upper arm-plates removes the form from that 

 doubtful genus. 



Description. — The length of the specimen is fy inch, and the 

 body is -^ inch iu diameter. 



The disk is circular in outline, is swollen inferiorly in the inter- 

 brachial spaces, and is slightly tumid on the upper surface. 



The radial shields are small, longer than broad, broadest aborally, 

 and they are separated orally by one or two plates. A central 

 rosette of six subequal plates has the central one pentagonal in 

 shape, the others being more or less rounded. Around the 

 rosette is a row of alternately large and small plates ; the smaller 

 fit in between the radial shields, and the others cover much of the 

 interradial spaces, there being only another row reaching to the 

 margin of the disk. A microscopic, transparent, cellular scaling 

 covers the plates of the disk and the spaces between them. There 

 are no long spines to the disk nor accessory scales ; but the radial 

 shields are covered with short, broad-based, bulging, conical 

 spinules, terminating in three small glassy thorns. Similar 

 spinules exist on the edges of all the plates of the rosette, and 

 rarely on the minutely scaled derm between them, and also, usually, 

 on the plates which separate each radial shield from its fellow. 

 The spinules increase in number towards the margin of the disk 

 and become crowded there. 



Beneath the disk and in the interbrachial spaces the spinules 

 are there abundant, and they are close externally, but rarer near 

 the mouth-shields. A small scaling separates the mouth-shields 

 from the spinulose part, and there are no large plates on the under- 

 part of the disk, which appears to be covered with skin. 



The generative slits, two in each space, are large and wide, and 

 reach to the sides of the mouth-shields. 



The mouth-shields are small, more or less irregularly lozenge- 

 shaped, broader than long, the aboral edge being broadly curved or 

 produced into a blunt angle, and the oral angle being more acute 

 and less pronounced. The madreporic shield is more rhombic 

 in shape than the others. The side mouth-shields are small, 

 narrow, slightly enlarged at the ends, and the oral margin is slightly 

 concave ; they do not quite unite within, and they do not reach 

 far across, below the arm-plate. 



The jaws are short and stout, separated slightly, and each angle 

 is widely apart from its neighbours. 



There are no true mouth-papillae, but a small flat spine with 

 a ragged top is situated on the side mouth-shield close to the 



