THREE NEW SPECIES OF METACRINUS. 413 



of the arms arc not only entirely devoid of any ambulacral skeleton, but they bear quite 

 small and rudimentary pinnules, which consist of only two or three minute joints, and 

 appear to remain permanently in this aborted condition (PI. LI. fig. 1). 



Some of the arms, however, have been broken at a syzygy and subsequently repaired, 

 so as to be still in a state of growth, as is shown in PL LI. tig. 5. The manner in 

 which their terminal portions, and those of the growing pinnules, are coiled up, as it 

 were, is very singular, and forcibly recalls the characters of the arms and pinnules in 

 Holopus. 



3. Metacrinus Stewarti, sp. now (PI. LII. figs. 13-18.) 



Stem robust and pentagonal, the internodes consisting of 11 joints, with moderately 

 crenulated edges. The joints are G millims. in diameter, and have slight horizontal 

 ridges on their sides, which are continuous round the angles, so that these are slightly 

 produced. The nodal joints increase in size from above downwards as far as the lower 

 ednes of the wide cirrus-sockets, and then diminish again. The intranodal joints arc 

 not grooved at all to receive the cirrus-bases ; while the suprauodals are markedly 

 incised, and contribute to form the upper portions of the cirrus-sockets proper. The 

 cirri are 50 millims. long, and consist of 50 stout joints, the basal ones being much 

 wider than their successors, which are all uniformly cuboidal. 



Remarks. — The characters of this stem-fragment are so well defined that I have no 

 hesitation in regarding it as belonging to a species of 3Ieiacriuus distinct from any yet 

 known ; and I am glad to have the opportunity of associating it with the name of my 

 friend Mr. Charles Stewart, P.L.S., to whom I am indebted for the opportunity of de- 

 scribing it. 



In the length of the iuternodes and in the peculiarities of the nodal joints it resembles 

 the stems of Metacrinus rotundas, 31. interruptas, and the ' Vega ' specimen. It is larger, 

 however, than all of these, especially the two last, and the joints have much more distinct 

 horizontal ridges. These give it a certain amount of resemblance to the stems of 31. 

 Wyvilliia.rL& 31. cingulutus, though it differs altogether from these two in the characters 

 of the nodes. 



Owing to the headless condition of the fragment, I was at first sight somewhat doubtful 

 as to which way up it should be placed. The line of union of the supranodal and the 

 nodal joints is rather less crenulated than usual, and looks almost like a syzygial line 

 between nodal and intranodal joints (PL LII. figs. 13, 18). 



The nodal joints (PI. LII. figs. 14, 18) arc enlarged, and increase in size from both ends 

 towards the cirrus-socket, which extends on to what I now know to be the supranodal ; 

 but it seemed possible at first sight that this might really be the intranodal, and the stem 

 belong to a Pentacrinus with the cirri directed downwards, instead of a 3Ietacriuus with 

 upward turned cirri, as is really the case. In fact, the nodal joints have no little resem- 

 blance to those of Pentacrinus Wyville-Thomsoui, widening downwards to the lower edge 

 of the cirrus-sockets, and then falling away again (PI. LII. fig. 18). This is also 

 the case in Metacrinus rotundas, though to a somewhat less extent (PL LII. fig. 5), and 

 the upward extension of the sockets on to the supranodal is somewhat more marked than 



SECOND SERIES. — ZOOLOGY, VOL. II. 66 



