REPORT ON THE CRINOIDEA. 343 



to receive the wide basal joints of the cirri ; so that its re-entering angles are deeper than 

 those of an ordinary internodal joint (compare PI. XXXIX. figs. 8, 9 ; and PI. LIII. 

 figs. 2, 4). The infra-nodal joints, however, are less deeply incised than those of Penta- 

 crinus, and are sometimes not modified at all, as in Metacrinus interruptus and 

 Metacrmus rotundus. This is the case in Pentacrinus wyville-thomsoni (PI. XIX. 

 figs. 3, 4), in which the lower edge of the cirrus-socket of the nodal joint projects out- 

 wards beyond the level of the infra-nodal joint below it, whde the supra-nodal is only 

 slightly modified to receive the bases of the upward projecting cirri. Traces of a similar 

 rim at the lower edge of the cirrus-socket are to be seen in Metacrinus interruptus 

 (PI. LII. fig. 2). 



I know of no characters by which isolated internodal joints of Metacrinus can be 

 distinguished from those of Pentacrinus, the relations of the teeth to the petaloid sectors 

 being the same in both types. But the number of internodals is much more constant 

 in Metacrinus than in Pentacrinus. In the latter genus there may be only one or two, 

 as in Pentacrinus maclearanus (PI. XVI. fig. 1) ; or about sixteen in Pentao-inus 

 asterius (PI. XL), and about forty in Pentacrinus wyville-thomsoni; whereas in Meta- 

 crinus the Kmits of variation are from six or seven in Metacrinus ivyvillii (PI. XLVIII.) 

 to thirteen in Metacrinus murrayi (PL XLII.) ; so that this character is of less value in 

 the classification of the species than it is in Pentacrinus. 



The geographical range of Metacrinus is much more limited than that of Pentacrinus. 

 Neither genus has been found in the Pacific east of long. 170° W.; but there are no 

 Atlantic species of Metacrinus. Pentacrinus was obtained without Metacrinus at 

 Stations 171 and 175 in the South Pacific ; while Metacrinus occurred alone at Station 

 209 (among the Philippines), and also in considerable abundance and variety at Station 

 192, in the Ai-afura Sea. It extends as far west as Singapore, and is represented by two 

 species in Japanese waters, where no Pentacrinus is known, excelling the doubtful 

 Pentacrinus mollis (PI. XXXIII. figs. 7-10). On the other hand, Metacrinus has not 

 been met with below 630 fathoms, while Pentacrinus has been dredged at 1095 fathoms 

 in the Atlantic, and 1375 fathoms in the Pacific Oceans. 



The mutual relations of the thirteen species of Metacrinus in which the calyx is 

 known, are shown in the following Table. The Challenger species are numbered 1 to 

 11, and the letters P. H. C. are appended to those which I have recently described 

 in the Transactions of the Linnean Society. The " Vega " specimen, which concludes the 

 list, has not yet been described. There are two other species of the genus (one obtained 

 by the Challenger) which are known as yet only by the characters of their stems ; and I 

 have therefore been obliged to place them in a separate list, as the number of radials in 

 the cup is still an unknown quantity. 



