MUSEU]M OF COMPAEATIVE ZOOLOGY. Iu3 



most mouth-papilla.* Mouth-shields small, as long as broad, shield-shaped, 

 with a well-marked obtuse angle inward and outer margin sometimes turned 

 down ; length to breadth 2 : 2.3. Side mouth-shields broad and thick, a 

 little widest at outer ends. Under arm-plates large, thick, and regular, much 

 wider than long, reaching at their outer edge entirely across the ai-m ; cleanly 

 curved without, re-enteringly curved on sides, and having a little peak within 

 where separated from next plate. Fir.st plate small, narrow wedge-shaped. 

 Upper arm-plates somewhat swollen, widely separated, wider than long, 

 bounded without by a gentle curve, and within by an obtuse angle or a deep 

 curve. Side arm-plates prominent and meeting freely above and below. Disk 

 thick and rising well above the arms, with a very deep, narrow constriction 

 and furrow in ea(;h interbrachial space. The space between this furrow and the 

 radial shields is on either side occupied by four large plates running diagonally 

 inward, whereof one or more are often broken in two. The central disk is 

 sunken, and covered by small, coarse, irregular scales, which, with the larger 

 plates, are sparsely beset with short, blunt, usually smooth stumps or spines, 

 which form also an irregular clump over each arm. Radial shields deeply sunken 

 in a furrow, widely separated by a high ridge of ii-regular scaler, much longer 

 than broad, presenting an acute angle inward ; length to breadth 3 : .8. Near 

 base of arm six stout, very thorny, glassy, blunt, cylindrical arm-spines, the 

 lowest ones much the stoutest ; lengths to that of an arm-joint 3.6, 3.6, 2.8, 

 1.7, 1.7, 1.7 : 1.2." Two thirds out on the arm the spines are more slender, 

 and the second much longer, attaining to 5 mm. The under spine is marked 

 by its thickness ; beyond base of arm it is somewhat curved. Tentacle-scales 

 large, thick, pointed, flattened, sensibly smooth, except towards end of arm, 

 where they bear two or three microscopic thorns. Color in alcohol, dull straw. 



It is not easy to say how much of the peculiar creasing of the disk and sinking 

 of the radial shields is due to the contraction of the animal drawn from a depth 

 and immersed in strong alcohol, and how much is natural. Of nine specimens 

 one had i-adial shields much wider and more nearly on a level with the disk ; 

 but in the rest the radial shields were deeply sunken. Six specimens from 

 the "Blake" expedition (Agassiz and Sigsbee, 1878) seemed a variety of" this 

 species. They were from 480 to 860 fathoms, near Cuba. All had the radial 

 shields not at all sunken and of a broad pear-seed shape ; only the centre of 

 the disk bore stumps, which were little articulated cylinders bearing a crown 

 of thorns. The largest specimen, with a disk of 8 mm., had seven arm-spines, 

 which were stouter than in " Challenger " specimens and shorter, their lengths 

 being 2, 3, 2.2, 2, 1.5, 1.5, 1.2 ; and the lowest spine, though thick, was 

 scarcely or not at all curved. The other specimens were young, and had long 

 slender arm-spines, and the under one curved. The " Challenger " specimen 

 from Station 33 resembled these. 



Station 3, 1530 fathoms, 3 specimens. Station 33 (var. ?) 300 fathoms, 3 

 specimens. Station 84, 1124 fathoms, 3 specimens. 



* The nomenclature of the various papilhc of the mouth is of course conventional. 

 In most cases the lowest tooth may also be called the innermost mouth-pai)illa. 



