Affinities of Trilobites. 



21 



Aberrant Group. 



Edriophthalma, Leach. 

 Animals having their 



eyes sessile. 



Orders, 

 r Amphipoda, Lat. 



Trilobita, Brongn. 



Entomostraca, Lat. 



Head distinct with 

 four antennae. Feet 

 thick andcrustace- 

 ous. Animals not 

 undergoing meta- 

 morphosis. 



Head distinct without 

 antennae. Feet ru- 

 dimentary, soft, and 

 membranaceous. 



Head rarely, if ever, 

 distinct from tho- 

 rax, but provided 

 with antennae. Feet 

 always distinct. 

 Animals undergo- 

 ing metamorphosis. 



With regard to the habits of true Trilobites^ these animals 

 have been supposed by some naturalists to be parasitical ; but 

 I conceive this hypothesis not to be very tenable, since almost 

 all existing articulated parasites that adhere externally to other 

 animals have strong feet, hooked at the end for that purpose. 

 Now the Trilobites certainly had no such strong crustaceous 

 hooks to their feet, or these hooks would have long since been 

 detected. The close affinity of Trilobites to Bopyrus does not 

 prove a parasitical mode of life, for Sphceroma and other Cymo' 

 thoad(B which, like Trilobites, have the power of coiling them- 

 selves up into a ball, are not parasitical, although so close in 

 affinity to the parasitical genus Cymothoa, Nay, it has been 

 said that the Cymothoadce and Epicarides do not draw their 

 nourishment directly from the animals to which they adhere ; 

 but, on the contrary, live entirely on the animalculae brought 

 to them in the water by the play of the branchiae, near which 

 they always take their post. Still the close connexion of Tri- 

 lobites with Bopyrus, and their feet almost null, if not entirely 

 so, induce me to think that these animals must have been to a 

 certain degree sedentary. The flat under surface of their bodies, 

 and the lateral coriaceous margin of several species, which is 

 so analogous to that of Chiton, make it probable that they ad- 

 hered with a soft articulated underside either to rocks or fuci. 

 They appear to have been among Crustacea what the Vermes 

 or white-blooded worms are among Ametabola, — often without 

 eyes, and always without antennae or distinct feet. If they 

 had feet, as Audouin and Goldfuss imagine, and, as indeed is 



