64 ON THE ECHINODERMATA OF THE 



their very distinct oral reentering curve, produce as a series a beautiful festooning, 

 the well-developed front lower arm-plate entering into the circle ; for the side mouth- 

 shields come up close to its flanks. 



The jaws are small, short, narrow, and gibbous inferiorly, and are fringed with 

 mouth-papillae, one of which, or the homologue of a tooth-papilla, is large and 

 solitary. This is larger than the others, is often spear-headed ; and there are usually 

 three smaller ones on either side of the jaws. As a rule, all these mouth-papillse vary 

 much in size and shape, and project obliquely downwards. The true teeth are angular 

 and broadly spear-headed in outline ; and they are in a single series of at least five. 



The first lower arm-plate is either unlike the others in shape and is perfectly or 

 irregularly elliptical, being broader than long from the oral to the aboral edge, or it is 

 heart-shaped and broadest distally and truncated orally. The second and lower arm- 

 plates are triangular, broad distally, where there is a bold curve, and angular orally, 

 the sides sloping, with scarcely any reentering curve ; the length and breadth are about 

 equal. The next and following plates retain their oral angle and broad distal curve, 

 which is sometimes notched in the median line ; but the sides near the distal corners 

 are at first parallel and form a space for the tentacle, and then they slope in with more 

 or less of a reentering curve to the angle. Far out they become smaller and smaller 

 and fan-shaped, with reentering curves on the sides, and often have a slight notch. 



The side arm-plates unite under the arm, and become longer and longer until they 

 occupy most of the under surface. After the fourth or fifth tentacle-opening there 

 is one small scale, or, rather, conico-cylindrical and blunt small spine. The first 

 visible tentacle-opening has four, and rarely five, scales on either side of it ; the next 

 has some (three) rudimentary scales on the lower arm-plate, and one larger and flat 

 scale on the side arm-plate ; under the next lower arm-plate there is often a rudimentary 

 scale, besides the fully developed one on the side arm-plate. 



The arm-spines, three in number on mid arm, are slender ; and the upper one is 

 the longest. There is a row of blunt and distinct small spinules (much smaller than 

 those in relation to the radial shields) on one side of the generative slit ; but they are 

 large in relation to those of other species. 



Lyman, after noticing that Ophioglypha robusta differs from the other species of 

 the genus in its short, broad mouth-shields and finely tapering arms, states that it has 

 been found even in the high latitude of Wellington Channel. He quotes A. E. 

 Verrill, who states that its range generally is from low-water mark to 18 fathoms. 

 Lyman's description of the typical specimen and of some varieties may be read with 

 great advantage. 



Description of the Illustrations of this Species on Plate IV. 



Fig. 5. The species, natural size, from above. 



6. The under surface of the disk : magnified 

 7. The upper surface of the disk : magnified. 



