194 ZIESENHENNE 



granulation. The arm-spines are longer, but still number only five, with 

 the arm length now averaging 3 times the disk diameter. 



At the 6 mm stage only the disk and mouth parts are granulated ; all 

 arm plates and the oral shields are free of granules. Six arm-spines are 

 now present and the arm length is 3 to 3.5 times the disk diameter. The 

 white arm banding is confined to the distal third of the arms. 



At the 8 mm disk diameter stage, 7 arm-spines appear; at 10 to 11 

 mm, 8; at 17 mm, 9; and at 20 mm, the full number of arm-spines is 

 present. Specimens exceeding 15 mm in disk diameter have an arm length 

 of 3.5 to 4 times the disk diameter. 



The color phases of O. panamense have been discussed by Ives ( 1889, 

 p. 76), Nielsen (1932, pp. 328-330), and H. L. Clark (1940, p. 343). 

 There appear to be three dominant phases with numerous variations. It 

 would be difficult to name sub-species or varieties that would be dis- 

 tinctive in large series, as the color seems to be the only difference in the 

 specimens. Rather than add more names, it is preferable to refer only to 

 color phases. 



The commonest and simplest color combination is that observed by 

 Lockington (Ives, 1889, p. 76) in which the disk is brown to olive and 

 the arms greenish, with the arms banded distally with white. There are 

 3 or 4 white bands in small specimens and up to 8 or more in adults. 

 Some 1740 specimens of this phase were collected in the Gulf of Cali- 

 fornia and south to Tangola Tangola Bay, Mexico. They prefer sandy 

 or muddy inter-tidal areas, still water, tidal pools, lagoons, etc., where 

 they are found in large numbers under rocks, coral clumps, and algae 

 holdfasts. Some specimens have broken upper arm plates and broken 

 and regenerating arms, indicating that they might have been crushed by 

 moving rocks. A few such animals with crushed upper arm plates might 

 be confused with O. teres, but the white arm bands are a distinctive 

 character for separating this form. The majority of the specimens of this 

 color phase have concealed, or partially concealed, radial shields. 



A second color phase, of which 122 specimens were taken in the Gulf 

 of California, seems to be associated with coral heads or rock shingle 

 beaches usually free of sand and mud and is the most colorful of all 

 littoral species. In general structure it appears heavier and more robust, 

 with stouter arms and with the radial shields exposed except occasionally. 

 This is probably because of its more exposed habitat. At nine stations it 

 was taken along with specimens of the green color phase, the latter being 

 the more numerous. The disk may be brown, gray, green, mottled or 

 splashed with tan, white, yellow, old rose, carmine, brown or light green. 



