THE STRAIT OF MAGELLAN. 75 



Where the beach was free from stones and formed of fine 

 sand, I picked up many specimens of a species of a very re- 

 markable genus of Isopoda, of which about half-a-dozen species 

 have been described from South America, and all, save one 

 which is found on the Chilian coast, from Patagonia, Fuegia, 

 and the Falkland Islands. This was the Serolis Orhigniana, 

 of which I give a sketch. It is closely allied to the S. 

 Fdbricii, the type of the genus, but differs from that species 

 in having the extremity of the last segment of the pleon 

 deeply excavated instead of presenting a rounded tip. In 

 common with the other members of the genus, it certainly 

 presents a wonderful resemblance, at first sight, to the extinct 

 Trilobites, of which it was at one time supposed to be an ally, 

 though differing widely from them in certain important points, 

 such as the possession of well-developed limbs and long 

 antennae. 



Pursuing our way along the shore I picked up many 

 fragments of a large crab, of which I afterwards obtained 

 excellent specimens. This was a species of Lithodes, the L. 

 antarctica, much like our northern European species, L. arctica, 

 but sufficiently distinct from it, and attaining a considerably 

 greater size. It is one of the commonest of the Crustacea 

 of the Strait of Magellan, and on the west coast of South 

 America extends as far north as the island of Chiloe, where I 

 saw it. Like the other species of the genus, the pleon or 

 tail-flap of the female is orbicular in form, and remarkable 

 for its enormous development and the absence of bila- 

 teral symmetry exhibited in its shelly plates ; those of the 

 left side, which alone bear the pleopoda or ovigerous ap- 

 pendages being double (or even more) the size of those on the 

 right. The animal is of a bright brick-red or scarlet colour, and 

 the carapace and limbs are armed with strong spines, which. 



