176 OUR COMMON BRITISH FOSSILS. 



on account of the three lobes of joints which usually 

 run along the body. Still, their crustacean origin had 

 been guessed at by bold speculators, and even Lin- 

 naeus classed them among the Entomostraca. 



How utterly at sea the majority of naturalists were 

 as to the true nature of these singular fossils is indi- 

 cated by some of their generic names. Agnostus, 

 Asaphus, Calymene, etc., the commonest of these, are 

 only Greek words signifying " unknown," or " con- 

 cealed," etc. Still, since the time of Brongniart they 

 have been universally regarded as crustaceans, and 

 the universal opinion is that they are allied to the 

 Isopoda, only that they were legless. Dr. Henry 

 Woodward, F.R.S., who has taken up Mr. Salter's 

 investigations among the Trilobites with great en- 

 thusiasm, believes he has detected evidences of legs 

 on the under side of some specimens, and his belief 

 has recently been confirmed by the discovery of Trilo- 

 bites with legs in America. Other naturalists think 

 these members are only the remains of "calcic arches." 

 The extinct Trilobites really represent a defunct order, 

 and as such we usually find them arranged in system- 

 atic works on Zoology. In that case they come in as 

 " missing links " between the Isopoda, of which the 

 common woodlouse (Oniscus) and the shrimp-para- 

 site (Bopyrus) are familiar types, and the Merostomata 

 of which the well-known "king-crabs" (Limulus) are 

 examples. The larval state of the higher classes in 

 the same order frequently resembles the adult condi- 



