244 HISTORY OF BRITISH CRUSTACEA. 



Fam. SPHMROMIBM 



Thorax of seven distinct segments, generally all capable 

 of motion; seven pairs of legs almost equally developed. 

 Abdomen very large ; the five first rings of the abdomen 

 slightly developed, and generally united; the last false legs 

 terminating in one or two plates, the outer one only mov- 

 able. Head large and transverse. The legs only adapted 

 for walking. 



Most of the species can contract themselves into a bail 

 when alarmed, and some of them have the power of making 

 holes in the softer rocks. 



Gen. 124. SPILEBOMA, Latr. 



Eyes not reaching the front margin of the first segment 

 of the body. Body seven-jointed. Tail entire at the tip, 

 the base on each side furnished with two equal leaf-like 

 appendages ; outer plate of last false legs folded under the 

 inner one. 



Dr. Johnston (Zool. Journ. iii. p. LSI) describes the S. rn- 

 (jicauda as swimming with considerable velocity, and often 

 on its back. It contracts itself into a ball when alarmed ; 

 and it can live a considerable time out of the water. 



