122 CRUSTACEA. 



ORDER VIII. — TRILOBITA. 



This order consists of a very extraordinary tribe of 

 extinct animals, known in this country under the name 

 of Dudley fossils, having the body composed of three trans- 

 verse parts, and divided longitudinally by two deep im- 

 pressions, forming three elevated lobes. The anterior part 

 of the body is generally more or less semicircular or lunate, 

 having on the upper side two large and generally reticulated 

 eyes, shaped like kidneys. This part is succeeded by nume- 

 rous (from six to twenty-four) transverse segments, and the 

 body is terminated by a large semicircular plate, less dis- 

 tinctly articulated than the preceding part. No organs of 

 locomotion or antennae have been observed, and it appears 

 to have been the habit of these animals to roll themselves up 

 into a ball by bending the extremity of the body beneath the 

 breast, and bringing it into contact with the head. Much 

 diversity of opinion has been entertained amongst naturalists 

 as to the relations in nature of these curious creatures. Ac- 

 cording to M. Adolphe Brongniart, who published a good 

 monograph of them, they are most analogous to the Limuli, 

 and other entomostracous Crustacea, provided with a great 

 number of legs, of a more or less membranous construction, 

 and which, it may be readily conceived, w ould have been 

 entirely destroyed during the great overthrow w^hich has 

 reduced these creatm-es to their present state. This opinion 

 has been strenuously maintained by Audouin. It is, how- 

 ever, opposed by Latreille, who observes that, supposing 

 these animals to have been destitute of legs, they would na- 

 tiu-ally approach the Oscabrions (or gasteropodous Chitons) ; 

 or rather, that they constituted the primitive type of annulose 

 animals, uniting on one side the last-mentioned molluscous 

 creatures with the entomostracous Crustacea, as w ell as with 

 the genus Glomeris (amongst the myriapodous insects) ; add- 



