A MONOGRAPH OF THE EXISTING CRINOIDS 315 



carination of P D only being visible exteriorly between them; synarthrial tubercles are 

 usually prominent. 



The 20-25 arms are 150 mm. long. The first brachial is slightly wedge-shaped, 

 short, about three times as broad as its exterior length, almost entirely united inte- 

 riorly. The second is of about the same size, but more pronouncedly wedge-shaped. 

 The first syzygial pair (composed of brachials 3+4) is oblong, half again as broad 

 as long. The next five or six brachials are oblong, nearly or quite four times as broad 

 as long, and those following slowly become wedge-shaped and later almost triangular, 

 four times as broad as long, soon becoming wedge-shaped again and, in the distal 

 half of the arm, oblong and very short, though somewhat longer again terminally. 

 The proximal discoidal brachials are somewhat swollen, and most of the brachials 

 have slightly overlapping distal ends. 



Syzygies occur between brachials 3+4, again from between brachials 13 + 14 

 to between brachials 31+32 (usually somewhere between the sixteenth and twenty- 

 fifth, with sometimes an extra one from two to four or five brachials beyond the first), 

 and distally at intervals of 2 to 13 (usually 8 to 12) muscular articulations. 



P D is 7 mm. long, moderately stout basally but tapering rapidly and becoming 

 slender in its distal half, with about 25 segments, which at first are three times as 

 broad as long, becoming twice as broad as long at the sixth, and squarish in the 

 terminal portion; some of the lower segments are bluntly carinate. Pi is 10 mm. 

 long with 30 segments, slightly less stout basally than P D and tapering somewhat less 

 rapidly; the segments are at first about twice as broad as long, becoming as long as 

 broad on about the eighth, and somewhat longer than broad terminally. P 2 is 15 

 mm. long, stouter than P 1( tapering evenly to a delicate tip, with 30 segments which 

 at first are about half again as broad as long, become squarish on the eighth or ninth, 

 and are about twice as long as broad at the tip. P 3 is 22 mm. long, stouter than the 

 preceding, with 30 segments, which at first are broader than long, becoming squarish 

 on the tenth, and longer than broad terminally; the pinnule is more or less carinate 

 in its proximal half, and has a moderately developed supplementary ridge on the distal 

 half of the outer side. P 4 resembles P 3 but is very slightly longer and proportionately 

 stouter and more carinate. P 5 is like P 3 . P 8 is 10 mm. long, resembling Pj but some- 

 what more strongly carinate proximally. The following pinnules gradually decrease 

 to 7 mm. in length and lose the basal carination, then increase to 12 mm. distally. 

 On some arms P 6 is small as described for P 8 , and again P 4 may also be small, while 

 occasionally P 2 and P 4 are similar, and P 3 is greatly enlarged ; sometimes P 2 , P 3 and P 4 

 are as described for P 3 , P 4 and P 6 . On one or more of the inner arms of each ray P 3 

 is often much larger than on the outer, while the adjacent pinnules are reduced in 

 size. 



Notes. — The preceding description was taken from the specimen from Port 

 Blair, Andaman Islands, which served as the type of Amphimetra mortenseni. 



The six specimens from Kwala Cassan are all rather smaller than those from the 

 Andaman Islands and apparently are not quite fully grown. 



One has 24 arms 100 mm. long. One of the IIIBr series is 2, all the other division 

 series beyond the IBr series being 4(3+4). The cirri have 32-33 segments, of which 

 the longest are very nearly as long as broad. 



