1-84 Observations on Trilobiits. 



So little is known respecting the habits of the Limulus, that 

 the use of its spine is undetermined. In this state of absolute 

 ignorance, it may be permitted to conjecture that it is in 

 some measure an arm by which they seize or secure their 

 prey. In the Isotelus this part is double. Hence we might 

 infer that it had greater facilities for furnishing itself with food, 

 and this would in a degree render unnecessary, feet armed 

 with pincers, and partaking of the calcareous nature of the 

 body; or, from the existence of seta? on corresponding parts of 

 the Limulus, they may possibly have been accessory organs of 

 locomotion themselves, analogous to the setiferous pro- 

 minences in the class Annelides, which are described as feet 

 by the acute Savigny : or, possibly these frontal processes are 

 organs of defence. When attacked, this animal may roll itself 

 up into a ball, as indeed it is often found, (see PI. XII. fig. 1.) 

 and by some mechanism these processes may be inserted into 

 corresponding cavities in the tail, and thus retain permanently a 

 rolled position, presenting nothing but its calcareous covering to 

 the enemy : or, lastly, they may supply the place of antennae, 

 for which their form and contiguity to the mouth and brain, 

 would seem to render them peculiarly applicable. 



Whatever may have been their uses, there is no doubt that 

 we have at length discovered a large and not unimportant part 

 of the under side of the Trilobite. A more extended and minute 

 investigation of the anatomy and habits of the Limulus, will 

 hardly fail to throw much light on the present obscure history 

 of Trilobites, and we hope will confirm the positions we have 

 endeavoured to establish. 



Since the preceding was in type, we have had an opportuni- 

 ty of examining in the " Nova Acta Regise Societatis Upsa- 

 liensis" for 1821, a paper by Professor Wahlenberg, entitled, 

 -' Petrificata telluris Suecanse examinata." In this memoir, 

 the author has arrived at the same conclusion with ourselves, 

 as regards the analogy between the Trilobite and Limulus, 

 although from different considerations. 



