THREE NEW SPECIES OF METACBINUS. 439 



that dredged by the ' Vega ' in 1879, at a depth of Go fathoms, in the Bay of Yeddo. 

 Prof. Loven has been kind enough to send me some fragments of the stem, and also to 

 permit my friend Mr. "W. Percy Sladen, P.L.S., to make an investigation of the type 

 during his recent visit to Stockholm for the purpose of examining the collection of Star- 

 fishes in the Museum. I am greatly indebted to Mr. Sladen for the trouble which he 

 took, and for the careful and detailed description of the ' Vega ' specimen with which he 

 has furnished me. It has nearly the same number of internodal stem-joints as M. inter- 

 rupt us and M. rotundus, and the length of the primary and secondary arms is very much 

 the same as in these types. In the number of radials (six, with syzygics in the second 

 and fourth) it agrees with M. interruptus and differs from M. rotundus ; but it approaches 

 the latter form more nearly in the characters of the stem. 



Although the diameter of the stem-joints is less than in M. Interruptus, and still more 

 so than in J/, rotundus, they are not only relatively but absolutely higher than in these 

 species. They resemble the latter rather than the former in the slight amount of sculp- 

 ture on their sides, and in their more rounded pentagonal form. As in both these types, 

 the cirrus-sockets end well above the lower edge of the nodal joint ; but the syzygial 

 surface, though much less sharply pentagonal than in M. interruptus, is far from being 

 as regularly circular as in M. rotundus (PI. LII. fig. 3). 



In the robustness and other characters of its stem, therefore, M. rotundus is distin- 

 guished from the two species which seem to resemble it most, just as it is by the irregu- 

 larity in the number of radials. The plates of the cup and arms are altogether larger 

 than in most species of the genus, the only ones which approach it in size being AT. 

 angulatus, M. cingulatus, and M. nobilis, all from near the Ke Islands (Station 192). 



The pinnules borne by the radials and lowest distichals have especially stout joints ; 

 and the serrate appearance of their outer extremities, produced by the elevation of the 

 distal edge of each joint, is extremely well marked, so as to recall the distinctive features 

 of Pentacrinus asterius. 



The disk of M. rotundas is excellently preserved, and shows very well one of the special 

 characters of the genus, viz. the origin of the ambulacra of the large lower pinnules either 

 directly from the peristome, or from the five primary groove-trunks before they bifurcate 

 (PI. L. fig. 2). The intcrpalmar areas of the disk are paved with small plates, which are 

 pierced by the water-pores, but arc not quite so closely set as they arc in some of the 

 Pentacrinidoe and Comatuke; while there are few or no plates in the perisome at the 

 sides of the disk between the rays. The disk-ambulacra, however, are protected by 

 several irregular rows of plates, which in some places meet so closely over the middle 

 line of the groove that it is converted into a tunnel. This was the case, not only 

 on the arms, but also in the calyx-ambulacra of the Pakeocrinoids, whether the latter 

 were external, as in Cyalhocrinus, or still further covered by a solid vault, as in Actino- 

 crlnus. 



The arms have no anambulacral plates overlying the muscular bundles, as is so often 

 the case ; but the ambulacra are well protected by a double row of somewhat irregular 

 plates, in which there is more or less distinct evidence of bifurcation. This becomes 

 specially marked at the bases of the pinnules, where the proximal limb of the fork 



