276 



A REVIEW 01 THi: TBILOBITES. 



In order to assist the general reader in following the above des- 

 criptions, an outline figure with accompanying explanation u an- 



nexed. 



6— glabella. 



E K— 



F F — ficiai suture [see )? 2 above.] 



C C — cheeks; c c— fixed cheeks. 



A — body axis. 



PI. PL— pleura). 



P — pygidium. 



5. Probable habits and affinities. — Much is here unavoidably con- 

 jectural : for tbe habits and affinities of these extinct forms of life 

 are veiled, to a great extent, in an almost impenetrable obscurity. 

 The following are, perhaps, the only really undebateable points con- 

 nected with the inquiry. First, the trilobites were marine crusta- 

 ceans. Their evidently articulated structure and the character of 

 their shelly covering, combined with the compound eyes, which so 

 many of them exhibit, and with their geological conditions of occur- 

 rence, are sufficient to establish this. The possession of compound 

 eyes would alone serve to separate them from the oscabrions or 

 chitons, with which they were at one time placed by Lateeille and 

 other observers. Secondly, the trilobites were gregarious, living in 

 vast communities — as proved by the abundance of their remains in 

 areas of often very limited extent. From this, it has been imagined 

 by the well-known naturalist MacLeay, that they adhered in masses 

 one upon another, after the manner of many of the sedentary niol- 

 lusks ; but the large compound eyes, the ornamented and frequently 

 spine-bearing shells, and the symmetrical habitus, are broadly op- 

 posed to this view. Thirdly, feet were either absent, or, if ever 

 present, were of a more or less rudimentary, soft and perishable 

 nature. No traces of these organs, nor of antenna 4 , have yet been 

 found : although from time to time imaginary discoveries of such 

 have been announced.* Fourthly, the trilobites were able, to a cer- 



Sen more especially plate 2 in Castelnau's Essai sur le Bysteme Silurian da PAmefiq.ua 



Septentriouale: 1843. 



