338 Prof. F. J. Bell on Bntish Opliiurich. 



In his invaluable critical study of the Ophiotriches of 

 European waters Lyman [t. c. pp. 240-250) indicates some of 

 the characters of 0. Luethem, as he does also in his " key" 

 to the species of Ophiothrix which he gives in his Report on 

 the ' Challenger ' Ophiurids ; but, as I have already said^ no 

 definite specific diagnosis has been drawn. 



Before going any further it is necessary to interpose a few 

 words as to the name to be given to our common Britisli 

 species. Mr. Lyman was able to distinguish between the 

 northern O.fnigilis and the southern 0. pentaplnilla^n ; but, 

 only a little later, he reports '■'0. penta-phyllum'''' from the 

 Faroe Channel. This single little fact will show the great 

 difficulty in discriminating and naming specimens of Ophio- 

 thrix better than any statement of mine. With all respect to 

 Mr. Lyman I must be allowed to say that Dr. Llitken's views 

 as to the identity of 0. fragilis and 0. pentaphyllum seem to 

 represent better the facts of the case ; and as 0. fragilis is 

 the older name, I shall henceforth use it for the common 

 British Ophiothrix. 



Though varying somewhat in size, 0. fragilis is never a 

 large species ; 0. Luetkeni may be roughly said to be twice 

 as large. In the former the upper surface of the arms is 

 distinctly keeled, each upj)er arm -plate projects forwards, and 

 its aboral end is knobbed ; these are some of the most charac- 

 teristic marks of 0. fragilis^ but they seem to be altogether 

 wanting in 0. Luetkeni. The possession of minute spines 

 by these upper arm-plates in the latter has been noted by 

 Mr. Lyman, and is a very fairly constant character. The 

 spines seem to vary more than he imagined^ for tliere are 

 specimens in which the stunting of the spines is so general 

 that it is difficult to believe it is artificial. 



It will, perhaps, be most convenient if I attempt first of all 

 to draw u)) the specific diagnosis of the better-known species 

 and then give one for 0. Luetkeni. 



Ophiothrix fragilis, L. 



A species which exhibits the greatest variations in colour 

 and marking and in the presence or absence of spines from 

 the disk ; of moderate size. 



Arms very fragile, about eight to twelve times as long as 

 the radius of the disk. The scales on the upper surface of 

 the disk often form projecting spinules, but may be almost 

 com])letely hidden by elongated delicate spines ; the inter- 

 rachial spaces below covered with fine spines. The trian- 

 gular radial shields are of large size and are bare, except for 



