132 NOTICES OF NEW BOOKS. 



Having determined this, the author proceeds to trace the ana- 

 logies between the Trilobites and the genera Apus and Branchipus, 

 and others of the Phyllopoda, with a view of working out more 

 accurately the affinities and the true place of the group. He 

 concludes, that the Trilobites form a family nearly allied to the 

 Phyllopoda, approaching this latter family most nearly in the 

 genus Branchipus ; and, therefore, forming a link between the 

 Phyllopoda and the JPcecilopoda. 



The Trilobites having been articulated animals, must necessarily 

 have cast their shell from time to time ; and it has been already sug- 

 gested by other naturalists that many fossils of this tribe, apparently 

 new, are only the exuviae of known species. It becomes important, 

 however, with reference to the habit of the animal, to determine 

 what transformations it underwent, since all the Phyllopoda to 

 which they seem so nearly allied undergo metamorphosis chiefly in 

 the anterior part of the body. They leave the egg as unarticulated 

 pyriform animalcules, and change considerably in appearance as 

 they pass through their course of existence. It is the opinion of 

 Dr. Burmeister, that a similar series of changes was undergone by 

 the Trilobites, and that the so-called genera Battus and Agnostus 

 represent only the shells of the young individuals of different 

 species ; and he explains at some length the reasons which have 

 induced him to arrive at this conclusion. He also alludes to some 

 other genera of the Palaeozoic period presenting analogies with 

 these singular Crustaceans ; and concludes by stating, that we 

 are perfectly justified, from the present state of the evidence, in 

 forming an opinion concerning the habits of the animal. He 

 states : — 



1. That they moved by swimming, and inhabited deep water; 

 but by no means crept on the ground at the bottom of the sea. 



2. That in the natural position of swimming the belly was above 

 and the back undermost ; and that the power of rolling itself into 

 a ball served the animal as defence against injury. 



3. That its food was the smaller marine animalcules ; or, in the 

 absence of other prey, that it 'devoured the young of its own 

 species. 



4. That it probably did not inhabit the depths of the sea, but 

 dwelt near the coast in shallows, and in innumerable multitudes ; 

 the individuals of one species herding together. 



5. That in spite of the incredible multitude of individuals, the 

 total number of species seems to have been small ; and that in this 

 respect Trilobites resemble the Phyllopoda, which, in spite of their 

 individual abundance, belong to not more than a dozen species, 

 although these are referred to as many as six genera. 



6. The great difference in size observable in existing Phyllopoda 

 renders probable a similar difference among the ancient Trilobites, 

 so that very unusually large individuals do not necessarily require 

 the introduction of a new specific name. 



D. T. A. 



