PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 135 



With pinnules replaced by or transforming into arms: In one specimen, as de- 

 scribed by Mortensen, the anterior and left anterior arms are quite normal. On the 

 right anterior ray the anterior arm has PI and P a transformed; P a bears only two lateral 

 branches near the tip; Mortensen remarks that it can scarcely be said that these 

 represent true pinnules, since they suggest much more strongly simple brandling; P : 

 has developed into a true arm almost as large as the arm which bears it. The four 

 lowest segments retain the character of pinnulars; on the fifth a pinnule is developed, 

 and from this point on the segments assume the character of true brachials, carrying 

 pinnules in the normal way. The portion beyond the sixth pinnule is lost. There 

 are no syzygies in the part preserved. The two lowest pinnules have the character of 

 oral pinnules; from the third onward tentacles are developed, but none of the pinnules 

 preserved carry gonads. The posterior arm of the same ray (the right anterior) also 

 has both P[ and P a transformed. PI has developed into a small but true arm with the 

 pinnules beginning on the eighth segment. The tip is broken off ; the portion remain- 

 ing bears three pinnules on each side of which the second has the tentacles developed. 

 P a has developed into a true arm larger than that into which P : has become trans- 

 formed, but distinctly more slender than the main arm. The pinnules begin on the 

 fourth segment. The tip is broken. The preserved portion carries 5 pinnules on 

 either side of which the lowest are developed as oral pinnules. In the right posterior 

 radius the oral pinnules of the anterior arm are normal, while on the posterior arm P ft 

 is developed into a small arm with the first pinnule on the eighth segment. The tip is 

 broken. The preserved part carries four pinnules on either side of which the first is 

 developed as an oral pinnule. In the left posterior radius both arms have both P, 

 and P s transformed into arms. On the posterior arm P : forms a small slender arm on 

 which the first pinnule is on the eighth segment; this is followed by two segments with- 

 out pinnules, then four with regularly alternating pinnules, another without a pinnule, 

 one with a pinnule, the remainder forming a pinnule-like tip provided with tentacles 

 like the other pinnules. P a has developed into a large arm very nearly as stout as the 

 main arm. The five proximal segments have the character of true pinnule segments; 

 the sixth bears a pinnule on the distal side, the seventh has no pinnule, and the eighth 

 bears a pinnule on the distal side; from this point onward the segments have the charac- 

 ter of true brachials and carry pinnules in the normal way; syzygies occur between 

 segments 9 + 10, 16+17, and then at intervals of 2 muscular articulations. The tip 

 is broken off, the preserved portion carrying eight pinnules on either side, not counting 

 that on the sixth segment. The lowest one on each side has the character of an oral 

 pinnule, although this is not very pronounced. None of the pinnules bear gonml-;. 

 On the anterior arm of the same ray (the left posterior) P! has very much the same 

 character as PI on the right anterior ray, with only four branches or pinnules in the 

 distal portion, the first occurring on the ninth segment. P a is developed into a small 

 arm, the pinnules beginning to appear on the fifth segment. The three lowest pinnules 

 are all on the same (the proximal) side; after the third pinnule there are four segments 

 without pinnules, then one with a pinnule on the distal side, after which the little arm 

 ends in a pinnule-like tip bearing tentacles like the usual pinnules. The lowest pinnule 

 on this arm bears tentacles and thus does not have the character of an oral pinnule. 



In another specimen, P! on the anterior arm of the left posterior ray is developed 

 into a small arm almost like that supplanting PI on the posterior arm of the left pos- 

 terior ray in the preceding. The 3 lowest pinnules are on the distal side, the first on 



