176 ECHINODERMS OF THE BRITISH ISLES 



ready for the bottom-life the young Ophiuroid throws off the larval 

 arms, whicli remain connected together and still go on swimming 

 for a little while, until the ciliated band disappears. The young 

 brittle-star is characterised by having a large, naked, rather 

 shining central plate ; young specimens are also apt to roll in 

 their arms on preservation. 



The very remarkable statement has been made that this 

 species may also develop in another way : directly, without any 

 pelagic larva (Apostolides) ; very likely this statement rests only 

 on misunderstood observations. The same, evidently, holds good 

 for the statement (Giard) that at certain times of the year it is 

 viviparous.^ 



In British seas Ophiothrix fragilis is very common all round 

 the coasts, mainly in shallow water, down to ca. 150 m. ; also 

 recorded from the Rockall Bank. It is otherwise distributed 

 from Lofoten and Iceland to the Mediterranean and the Azores, 

 and apparently along the whole African coast down to the Cape. 

 Its bathymetrical distribution is from the tide limit dowTi to ca. 

 350 m. 



2. Oj)hiotlirix Lutkeni Wyv. Thomson. (Fig. 99.) 



Disk with rather long spines, articulated to fairly distinct 

 tubercles. Radial shields with scattered, much finer spines. 

 Ventral side of disk with similar fine spines in a belt along the 

 mid-hne to the mouth shield. Dorsal plates 

 of arms with outer edge rounded, not pro- 

 duced, without a longitudinal keel or at 

 most with a very faint indication of a 

 keel ; they carry, in the proximal part of 

 the arms, scattered, fine spines, which may, 

 however, be wanting in younger specimens. 

 Ventral plates mainly as in 0. fragilis ; 



Fig, 99, Dorsal plates one small tentacle scale. Arm spines 



oi Ophiothrix Liitkeni. slender, finely thorny, 8 in the proximal 

 X 6. (From Dan , p i n ' i • • ^ 



mark's Fauna.) P^^t of arm, gradually decreasmg m number 



farther out ; they increase very gradually 

 in length upwards. Mouth shields transverse oval, distinctly 

 broader than long, with a small peak within and without. 

 It is a large and robust species, which reaches a size of ca. 25 mm. 



1 The same author also has maintained that most other Ophiuroids of 

 the Channel coasts are viviparous at certain times of the year, these times 

 being not more nearly indicated. It appears that this is all due to 

 erroneous observations, as is likewise the statement that they are also 

 hermaphrodites. 



