50 



BULLETIN 75, UNITED STATES NATIONAL MUSEUM. 



division of each radial shield into a light outer and a dark inner half. 

 This seems to be a helpful diagnostic mark for the species. One of 

 the most constant specific characters is the number (four) and rela- 

 tive size of the arm spines, and the absence of tentacle pores and 



Fig. 11.— Ophiuea maculata; adult, a-c, X5; young, d-f, X7. a and d, from above; 6 and e, from 

 below; c and /, stoe views of arm joints near disk. 



tentacle scales on the arms. The number of disk scales and the 

 form of the oral shields are unusually variable, while the radial shields 

 which are in contact in young specimens and in some adults are 

 often ver}^ widely separated from each other. The figures given 



