168 ECHIN0DERM8 OF THE BRITISH ISLES 



Ophiomyxa jyentagona Miill. and Troschel, is common in the 

 ^Mediterranean and along the African coast down to Cape Verde ; 

 but it has been found also at the north coast of Spain 

 (" Talisman "), so there may be a possibility that it occurs also 

 off the British south coasts. It is mainly a littoral form, but it 

 is known from depths down to 235 m. 



Key to the species of Ophiomyxa known from or likely to 

 occur in the British seas. 



Arm spines 5 or 4 (3) ; ventral plates with a deep notch in the outer 

 edge, well separated (Fig. 94, h) O. pentagona Miill. and Troschel 



Ami spines 4 or 3 (2) ; ventral plates broadly in contact ; no 

 notch in the outer edge (Fig. 94, a) . 1. 0. serpentaria Lyman 



1. Ophiomyxa serpentaria Lyman. (Fig. 94, a.) 



(Syn. Ophiodera serpentaria (Lyman).) 



Disk wholly naked. Marginal series of scales rather indistinct. 

 Mouth papillae three, more rarely four, generally increasing in 



Fig. 94. — Part of oral side of Ophiomyxa serpentaria (a) and three ventral 

 arm plates of 0. pentagona (6). x 6. 



size inwards. Mouth shield broader than long, with a rounded 

 peak inwards. Ventral plates produced laterally, broadly con- 

 tiguous. Pores large, decreasing in size outwards, without 

 tentacle scale. Genital slits reaching to about the fourth arm 

 joint. Arm spines mostly three, but there may be four in some 

 joints, only two in others^ and as they are not placed in the same 

 height on successive joints, even where the number is the same, 

 there is a good deal of irregularity in the arrangement of the 



