SPHiEROMA RUGICAUDA. 409 



having the eyes on each side, which do not touch the 

 external margins, and are not quite round in their out- 

 line ; the superior antennae are about half the length of 

 the inferior ; the flat basal joints are punctate ; the 

 segments of the body are nearly equal, short, and con- 

 vex ; the terminal segment of the tail is rounded behind 

 and obliquely truncate at the sides ; the two plates of 

 its lateral appendages are equal, of a linear-oval shape, 

 neither ciliated nor serrated on the outer edge. 



When alive, it is of an ashy colour, with dots and 

 streaks of black, and is often marked with a light 

 coloured stripe down the back ; it is much more active 

 than the preceding species, swimming with considerable 

 velocity and often on its back, and contracting itself into 

 a ball when alarmed ; it can live a long time out of 

 water. 



It occurs on the coasts of France and Great Britain. 

 Dr. Leach took it very abundantly on the island of Ulva, 

 near Mull (one of the Hebrides), and also at the mouth 

 of the River Tamar, in Devonshire. Dr. Johnston also 

 sent it to us from Berwick-upon-Tweed, and Dr. Kina- 

 han dredged it at Blockhead, in Belfast Bay. 



