A MONOGRAPH OF THE EXISTING CRINOIDS 301 



cross-banded with yellow, and the distal pinnules may be uniformly brownish yellow. 

 The cirri are yellow-brown, at least dorsally, but arc often more or less dusky or 

 purplish on the oral surface. In nearly all individuals, however, both old and young, 

 the terminal two or three segments, except the claw, have a dusky spot on the oral 

 side. This marking seems to be a very constant character in specimens from Tobago. 

 Occasionally individuals are found in which the pinnules and dorsal side of the arms 

 are plenteously besprinkled with silvery white, giving them an exceptionally handsome 

 appearance. 



All the small individuals found by Dr. Clark were brownish yellow or bright brown, 

 more or less marked and banded with purple, and this general coloration is not rare 

 in adults, particularly in those found under slabs of rock on Buccoo reef and in similar 

 shaded places. Some of these individuals were very handsome in their brilliant array 

 of purple and gold, and it was hard to believe that they were really identical with the 

 dull-colored individuals from the shallows of Buccoo Bay. 



A natural inference from the specimens seen is that the young are uniformly 

 yellow or bro^vnish yellow and that the purple pigment develops as they mature, in 

 some individuals completely obliterating the original color, but usually appearing 

 simply as spots, blotches, and cross bands. One could scarcely avoid the impression 

 that the development of the pigment is associated with life in the open sunlight, 

 but there was no opportunity for securing an answer to the interesting question 

 which suggests itself: Do the bright-colored individuals avoid the sun because they 

 lack pigment, or do they lack pigment because they have never lived exposed to the 

 sun? 



The largest specimens measured by Dr. Clark had an arm length of nearly 100 

 mm., and a few specimens exceeded that, but the great majority had arms from 60 

 to 80 mm. long. Several very small individuals were found under rocks on Buccoo 

 reef, but the smallest one seen, having arms about 18 nam. long, was discovered in a 

 clump of Corallina. 



Abnormal specimens. — Dr. P. H. Carpenter said that, except for a 6-rayed in- 

 dividual of Nenmetra pulchella (see Part 3, p. 137), the only 6-rayed comatulid he knew 

 of was a small dry Antedon in the collection of the British Museum. In this the disk 

 is sufficiently well preserved to show that the additional ray is inserted between the 

 two of the right side (D and E). Suspecting that this specimen might be an example 

 of this form I asked my friend the late Prof. F. Jeffrey Bell to be so good as to examine 

 it for me. This he very kindly did, and he wrote me that it was, as I had surmised, 

 a specimen of Tropiomeira carinata, but there was no record of the locality whence 

 it had come. 



Among 260 specimens from Rio de Janeiro in the collections of the United States 

 National Museum (6), the Museum of Comparative Zoology at Harvard College 

 (248), and the Yale University Museum (6) that I examined in 1907 I found no less 

 than 17 that are completely and perfectly 6-rayed (see Part 2, p. 82). None of those 

 from any other locality that I have seen have more than 5 rays. These 6-raycd in- 

 dividuals are all but one of comparatively small size with an arm length of from 50 

 to 60 mm., the exception having an arm length of 95 mm. and being the only one sex- 

 ually mature. In 12 of the 17 6-rayed specimens the disk can be examined \vithout 

 injury to the arms or pinnules. In three of these it is quite impossible to tell which 



