362 THE VOYAGE OF H.M.S. CHALLENGER. 



eighteen or twenty joints, the lowest of which are cuboidal. The next few, though still 

 very thick, are much flattened laterally and gradually diminish in width, with the lateral 

 edges of the dorsal surface raised and thickened. The terminal part of the pinnule 

 consists of much smaller joints, and is more or less distinctly serrate. In the pinnules of 

 the third and the next following distichals the dorsal surface of the two or three thick 

 basal joints is rather broad, but the following joints diminish rapidly both in breadth and 

 in thickness. Beyond the distichal axillaries all the pinnule-joints are longer than wide, 

 with the exception of the first two, which are much expanded, and this character is very 

 marked in all the following pinnules till about the level of the fourth axillaries. Beyond 

 this point the second and third jiinnule-joints more nearly resemble their successors, 

 though traces of the expansion of the first joint are visible for some distance farther. 



The disk (so far as it is visible) is well protected by plates, both on its ventral surface 

 and on its sides, right down to the h}^ozygal of the second brachial. The brachial 

 ambulacra are but little above the narrow arm-groove, and are protected like those of the 

 large lower pinnules by very irregular plates. The terminal pinnules have well defined 

 and rather jjointed side plates. 



Colour — a uniform dusky purple when fresh (Moseley) ; in spirit, light brownish- 

 white. 



Zoca^%— Station 214, February 10, 1875; off the Meangis Islands; lat. 4° 33' N., 

 long. 127° 6'E. ; 500 fathoms ; blue mud ; bottom temperature, 41°'8 F. Two specimens, 

 with Myzostoma wyville-thomsoni, von Graff. 



Remarks. — This elegant little species is the smallest Metacrinus which I have yet 

 seen, with the exception of Metacrinus nodosus ; and it has many points of resemblance 

 with that type, as will be explained later. Although the stem and cup are much less 

 robust than in Metacrinus wyvilUi, the number of arms is nearly half as large again as in 

 that species, which rarely has an axillary beyond the palmars ; while in Metacrinus 

 costatus this is generally the case on four out of the eight tertiary arms, and there may 

 be another axillary beyond the supra-palmar. The number of internodal joints is nearly 

 the same in the two species, being rarely less than seven in Metacrinus costatus, though 

 sometimes falling to five in Metacrinus ivyvillii. But they are totally difi"erent in their 

 form and external markings, as will be evident from a comparison of PL XLVII. 

 figs. 1-4, and PI. XLIX. figs. 3, 4. The nodal joints are also quite difi"erent in the two 

 species. The cirrus-sockets of Metacrinus wyvillii (PI. XLVII. figs. 1, 2) extend both 

 upwards and downwards on to the supra- and infra-nodal joints beyond the articular 

 facets, which occupy the whole height of the nodal joints. But this is far from being the 

 case in Metacrinus costatus ; and the nodal joints therefore are less deeply incised than 

 in Metacrinus wyvillii, while their angles are much sharper and more produced outwards 

 (PI. XLIX. figs. 3, 5). There is also a good deal of difi'erenee between the pinnules of 

 the two t}^es. Both those on the radials and distichals of Metacrinus wyvillii and those 



