XIPHOSURA. 795 



body, and the nature of the appendages, however, render it 

 highly improbable that the resemblance, striking as it at first 

 appears, has any phylogenetic significance. 



After the first moult the caudal spine begins to elongate, and 

 at this stage, while the abdomen re- 

 tains its segmented larval character, a 

 true affinity with the fossils Prestwichia 

 and Belinurus of the palaeozoic rocks 

 is clearly revealed. 



Four living species of King Crab 

 are known * : L. polyphemus from the 

 eastern coast of the United States, L. 

 longispinus from China and Japan, 

 and L. moluccanus and rotundicauda 

 from the East Indies. They frequent 

 muddy shores where the water is two Stlfii WtaS ^ 

 to six fathoms in depth, and often 



bury themselves in the mud. Their food consists of annelids, 

 such as Nereis, and bivalves. 



Fossil species of Limulus occur in Jurassic and Triassic rocks ; 

 while in the palaeozoic times an allied family, the Hemiaspidae, 

 existed whose members (Hemiaspis, Belinurus, Prestwichia) 

 resembled the young Limulus after its first moult. They may 

 hence be regarded as persistent larval forms. The abdomen 

 was much more completely segmented than that of Limulus, 

 and in Hemiaspis there is a division into pre- and post- 

 abdomen, affording a transition to the Eurypterida and the 

 Scorpions. 



On comparing Limulus with the Crustacea, with which it 

 has, until recently, been usually classified, we notice as conspicu- 

 ous points of difference the absence of appendages corresponding 

 with the first antennae, the division of the body into parts, of 

 which the anterior includes seven segments,! and the absence 

 of a stage of development corresponding to the nauplius larva. 

 The most definitely Crustacean feature is the biramous character 

 of the abdominal appendages ; and the existence of median 

 and compound lateral eyes makes, though less strongly, in the 



* See, however, Pocock, Ann. Mag. N.H. (7), 9, 1902, p. 256. 



t The development of the camerostome from paired rudiments raises 

 the question whether it is not the representative of a pair of appendages 

 anterior to the chelicerae (p. 323). 



