MONOGRAPH OF THE EXISTING CRINOIDS. 655 



into a number of variously sized polygonal areas, minute, or larger, and separated 

 by deeper furrows; or the skin may be covered by a quantity of small tubercles 

 pressed close together or separated by intervals into larger and smaller groups; 

 the tubercles may be of equal size, only diminishing slightly toward the borders, 

 or of very different dimensions; occasionally they become so minute and closely 

 packed that the skin acquires a granular appearance, while on the other hand they 

 are sometimes highly developed and arranged in radial lines. 



Von Graff states that the group of species containing the larger and stouter 

 forms displays most variety in color and sculpturing, though only on the dorsal 

 surface, the ventral surface being always of a uniform dull yellow or brown. The 

 species of the second group are nearly all yellow or brown, which are the pre- 

 vailing colors of the myzostomes, with a somewhat lighter colored margin. The 

 larger forms occasionally exhibit a pattern of two colors on the dorsal surface. 



Semper stated that he found Myzostomv/m glabrum (" tuberculosum"), which 

 is spotted with red and yellow, living only on variegated comatulids, while the 

 uniformly colored M. cirriferum he found only on red comatulids, which it matches 

 in color. 



Von Willemoes-Suhm recorded the presence, in the Arafura Sea, of black and 

 white spotted myzostomes living upon black and white comatulids. 



At Trieste von Graff examined 203 specimens of Antedon adriatica and found 

 black, yellow and whitish myzostomes just as commonly on red individuals as red 

 myzostomes on variegated individuals. 



In a special investigation of over 200 comatulids at Murray Islands, Torres 

 Strait, Lieutenant Potts found that blackish, yellow, and white myzostomes were 

 just as frequently to be found on red comatulids as blood-red myzostomes on varie- 

 gated comatulids. 



Lieutenant Potts states that the myzostomes found on the comatulids at the Mur- 

 ray Islands were very numerous and belonged to several species. They are in many 

 cases very brightly colored, and have pronounced color patterns. Generally speak- 

 ing, there are two types of pattern. In the first, concentric rings of bright and 

 dark pigment alternate; in the second, the dorsal surface is ornamented with 

 radiating ridges, and these are usually free from pigment or very light colored; 

 the ridges are thrown into relief by an edging of a dark pigment, purple or black. 

 The general ground color between the ridges as a rule approaches that of the 

 comatulid upon which the myzostome is found. 



One of these was very common on the dark green or black varieties of Coman- 

 thus annulatus. The alternate black and nonpigmented rings are in vivid contrast, 

 but the myzostome is thin and the nonpigmented parts are so transparent as to be 

 inconspicuous against the dark ground of the host. This species seems to occur 

 only on the darker crinoids. In another species the same arrangement is found, 

 but much lighter hues prevail, green pigment alternating with very light brown. 

 The colors of the host were not noted. 



When the host is very light colored the alternation of darker rings does not 

 occur. On a green variety of Coma/nthus annulatus a myzostome was found which 



