CLARK: BRITTLE-STARS. 295 



by Liitken, is one of the most constant and noticeable characters. 

 It is possible that two tentacle-scales rnay sometimes occur on the 

 first pair of pores but I have seen no such case. Ophiopus is very 

 near Ophiactis but is distinguished by the absence of genital slits. 

 Amphiura (and most other genera in the family) are readily separated 

 by the pair of subdental papillae, while Amphiactis has 3-5 oral 

 papillae on each side of the jaw, and 2 tentacle-scales. 



More than seventy specific names have been used in connection 

 with Ophiactis but 15 represent species which should be referred to 

 other genera. These are as follows: — 



Ophiactis canescens Liitken and Mortensen, 1899, is an Amphiactis 

 clavigera Ljungman, 1864, " " Ophiolebes 



dissidens Koehler, 1904, " " Amphiactis 



duplicata Liitken and Mortensen, 1899, " " Amphiactis 

 humilis Lyman, 1869, " " Ophiolebes 



lorioli Koehler, 1897, " " Amphioplus 



minor Doderlein, 1910, " " Amphipholis 



nigrescens Hutton, 1872, is probably an Ophiocoma 

 parata Koehler, 1904, is an Amphiactis 



partita Koehler, 1897, " " Amphiactis 



patula Lyman, 1879, " " Amphiactis 



pectoralis Lyman, 1880, " " Amphiactis 



picteti de Loriol, 1893, is probably an Amphiactis 



purpurea Meissner, 1901, is an Ophiothrix 



umbonata H. L. Clark, 1915, " " Amphiactis 



Three of the species in this list demand a little further consideration : 

 — 0. nigrescens Hutton has never had any adequate description as 

 no zoologist seems to have met with it in the past forty-five years; 

 0. pectoralis was well described by Lyman but has not been studied 

 since the Challenger Report was published, and actual comparison 

 of it with species of Amphiactis is very ..desirable; 0. picteti was con- 

 sidered by de Loriol, to be an Ophiocnida, from which genus the present 

 writer placed it in Ophiactis, but as it has two tentacle-scales on the 

 basal pores of the arm, it is debarred from that genus as here defined; 

 Koehler has seen specimens and regarded them as Ophiocnida but the 

 mouth-parts exclude them from that group, as they do indeed from 

 Amphiactis ; it is very possibly a new generic type. 



Of the remaining 56 specific names associated at one time or another 

 with Ophiactis, 21 are synonyms pure and simple of valid species. 



