CLARK: BRITTLE-STARS. 301 



. /, 



h Oral shields much wider than long; upper arm-plates 



with even margins and not at aU swollen mulleri 



h' Oral shields about as long as wide; upper arm- plates 

 swollen, distal margin often with 2 very slight notches, 



much as in 0. savignyi gymnochora 



Disk-scaling finer, 7 or more series in each interambulacral 

 area; these areas below, fully covered with scales; under 

 arm-plates squarish; 5 arm spines. 

 h Upper arm-plates inchned to be tetragonal, wider distally 



than proximally and somewhat angular maculosa 



h' Upper arm-plates distinctly ellipsoidal. 



i Oral shields much wider than long; adoral plates with 

 no distally projecting angle separating oral shields from 



side arm-plates resiliens 



i' Oral shields about as long as wide; adoral plates with a 

 distally projecting angle separating oral shields from 

 side arm-plates nomentis 



Ophiactis symbiota. 



H. L. Clark, 1916. Endeavour Ech., p. 88, pi. 36. 



Only a single specimen of this well-marked species is known and the 

 number of oral papillae, while apparently 2, is not certainly determined. 

 The disk-covering is, however, very distinctive. The type-locality 

 is in Bass Strait, Australia, 100-300 fms. 



Ophiactis plana. 



Lyman, 1869. BuU. M. C. Z., 1, p. 330. H. L. Clark, 1915. Mem. M. C. Z., 



25, pi. 10, fig. 1, 2. 

 Ophiactis flexuosa Lyman, 1879. Bull. M. C. Z., 6, p. 37. 1882. Challenger 



Oph., pi. 20, fig. 1-3. 

 Ophiactis perplexa Koehler, 1897. Ann. sci. nat. Zool., ser. 8, 4, p. 327, pi. 7, 



fig. 40, 41. 

 Ophiactis profundi Liitken and Mortensen, 1899. Mem. M. C. Z., 23, p. 140, 



pi. 6, fig. 4-6. 

 Ophiactis brachygenys H. L. Clark, 1911. Bull. 75 U. S. N. M., p. 135, fig. 51. 



A careful comparison of type-material of 0. plana, 0. flexuosa, 0. 

 profundi, and 0. brachygenys, with each other and with an excellent 

 specimen of 0. perjilexa, identified by Koehler, has satisfied me that 

 all represent a single species, and even the individual diversity is 

 very slight. The geographical and bathymetrical ranges are both 



