218 



ECHINODERMS OF THE BRITISH ISLES 



Both being littoral forms there is scarcely any prospect of finding 

 any of them within the Britisli area. A. neapolitana is dis- 

 tinguished from A . brachiata by having granulated radial shields, 

 semisqtiamata by having only 6 arm spines, 1 tentacle scale and 

 ventral side of disk naked. 



1. Acrocnida brachiata (Montagu). (Fig. 123.) 



(Syn. Amphiura, Ophiocnida, Amphiocnida brachiata (Mont.) ; 



Ophiocentrus brachiatus (Mont).) 



Disk covered with scales on both sides. Primary plates in- 

 conspicuous ; radial shields small, smooth, separated. Dorsal 

 arm plates very short, nearly rhombic ; ventral plates short and 



Fig. 123.- 



-Acrocnida brachiata ; part of oral side (1) and of dorsal side (2). 

 X 9. (From Danmark's Fauna.) 



broad, nearly rectangular, with sinuate excavated outer edge. In 

 the proximal part of arm they have a sharp median keel and a 

 pair of lateral keels ; these keels gradually disappear farther out 

 on the arm, the median keel being visible for a longer distance 

 than the lateral keels. Eight to ten (or even as many as 12-13) 

 short arm spines in proximal part of arms. Two tentacle scales 

 in the proximal part ; some distance beyond the disk the inner 

 (adradial) papilla disappears, while the outer one continues to 

 about the middle of the arm, diminishing in size. In the distal 

 half of arms there are no tentacle scales. Mouth shields spear- 

 head-shaped, with a conspicuous outer lobe. Outer mouth 

 papilla broad, scale-like, somewhat folded. Colour in life bluish- 

 or brownish-grey. Diameter of disk up to ca. 12-13 mm. ; arms 

 ca. fifteen times that length. 



