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ARTICLE XI, 
On the Morphology, Classification and Distribution of the Tri- 
lobites. By Dr. Emmericu of Meiningen*. 
[From Leonhard and Bronn’s Neues Jahrbuch fiir Mineralogie, Geologie und 
Petrefaktenkunde, 1845, Part I.] 
I. Morphology of the Trilobites. 
SINCE the first scientific researches of Wahlenberg no further 
serious contest has arisen with regard to the arranging of the 
Trilobites among the Crustacea. As Crustacea they possess a 
body divided by transversal articulation into several successive 
rings, which, with the exception only of the genus Olenus, Zenk., 
and of the doubtful genus Battus, are of a threefold kind, viz. 
the anterior rings are united, as in Limulus, into a large cephalic 
shield, of the size of the whole width of the body, the shield 
bearing the organs of feeling and of mastication. The central 
rings are freely moveable and form the thorax, which always 
possessed six or more feet on its under side, corresponding to 
the number of joints: the posterior rings are likewise united 
with one another into a larger or smaller caudal shield, on which 
was situated the anus. Thorax and abdomen correspond with 
the thorax and abdomen of the Jsopoda(wood-lice). The genus 
Olenus, already mentioned, is the only one which has homolo- 
gous rings behind the head ; so that there is between it and the 
other Crustacea a relation similar to that which exists between 
the Myriapoda (Scolopendra and Julus) and the Spiders. 
It is well known, that besides this tripartite division of the 
body into head, thorax and abdomen, there also exists a longi- 
tudinal division, separating the body into a central part and into 
the two sides. If we first consider the rings of the thorax, we 
find the two lateral portions, which adjoin the axis, to be free 
appendages, connected with the axis by perfect or imperfect ar- 
ticulation: these are the so-termed fins. These fins are hollow, 
adapted for the reception of muscles. Each of them probably 
corresponds with the two parts, which, in the rings of living 
Articulata, are designated pleure; with however the following 
distinction. Whilst in the latter they form part of the boundary 
of the cavity of the body of the animal, they are entirely ex- 
* The Editor is indebted to the kind assistance of Prof. J. Phillips for the 
revision of this Article. 
VOL. IY. PART XIV. T 
