RELATIONSHIP OF L1MULU8 TO TBIL0B1TE8. 303 



cently hatched Limulus (Fig. 271), that of Barrande's larva 

 ■of Trinucleus ornatus (Fig. 373, natural size and enlarged). 

 He will see at a glance that the young Trilobite, born -with- 

 out any true thoracic segments, and with the head articm* 

 lated with the abdomen, closely resembles the young Limu- 

 lus. In Limulus no new segments are added after birth ; 

 in the Trilobites the numerous thoracic segments are add- 

 led during successive moults. The Trilobites thus pass 

 ihrough a well-marked metamorphosis, though by no mrans 

 &o remarkable as that of the Decapods and the Phyllopods. 



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Tig. S71.— Larva of the Kinii-crab. 



Fig. 378.— Larva of a Trilo- 

 bite, THntbdeus ornatus.-^ 

 After Barrande. 



The young king-crabs swim briskly up and down, ekim- 

 ming about on their backs like Phyllopods, by flapping their 

 gills, not bending their bodies. In a succeeding moult, which 

 'Occurs between three and four weeks after hatching, the 

 abdomen becomes smaller in proportion to the head, and the 

 Abdominal spine is about three times as long as broad. At 

 "this and also in the second, or succeeding moult, which oc- 

 -curs about four weeks after the first moult, the young king- 

 crab doubles in size. It is probable that specimens an inch 

 long are about a year old, and it must require several years 

 ior them to attain a length of one foot. 



The Limuli of the Solenhofen slates (Jurassic) scarcely 

 differed in appearance from those of their living descend- 

 ants. 



Limulus, Prestwichia, Bellinurus, and Euproops form 



