BARRANDIA. 141 



facial suture takes place simultaneously with the increase of the body-segments. And the 

 very young Trilobite (Barrande has traced some of the species from the egg) looks like a 

 totally different genus from the adult ; it is a simple disk, which gradually only becomes 

 lobed, segmented, and provided with organs, as its life goes on and its size increases. The 

 Zoe of the crab is now familiar to us. But its discovery hardly excited more interest 

 among naturalists, than did Barrande's observations on the young Trilobites among palaeonto- 

 logists, when first announced in May, 1849, to the French Academy. My own far less 

 complete description was published in June of the same year. 



It seems that the additional segments always come in between the thorax and the tail, 

 while the latter also receives at each fresh moult an accession of segments till it attains its 

 full number. What becomes of the moulted crusts of Trilobites ? From all analogy they 

 should be cast off, slit open in some part of the dorsal region. And such specimens should 

 be looked for in our shaly rocks ; for it is impossible that they should be much more des- 

 tructible than the newly-formed crust. 



Description. — I have obtained from Mr. J. E. Lee's cabinet a much larger tail of this 

 species than we before possessed. And we may therefore reckon the species to have been 

 fully an inch and a half long, widely oval, with obtuse ends ; the head forming a semicircle, 

 longer than the body, and larger than the tail. 



The axal-furrows are parallel below, somewhat abruptly divergent above, and reach 

 the very narrow margin in front. The glabella is without lobes, or very obscurely lobed. 

 The cheeks, wider than the glabella, are gently convex, narrowly margined, and bear the 

 lunate eye so forward as nearly to touch the front margin, a character by wdiich B. radians 

 is easily distinguished from B. Cordai, next described. Head-angles very shortly spinous. 



The axis of the body is much narrower than the straight pleurae, which are grooved 

 three fourths of their length, and have the scarcely visible fulcrum placed at more than 

 half-way out from the axis. The tips are sabre-shaped. 



The tail is nearly a semicircle, and all but flat. And our largest specimen shows a 

 length of six lines by a breadth of ten lines. Of this length the conical axis occupies less 

 than three-fourths ; and but for the triangular appendage (appendix) beyond its bluntish 

 tip, does not reach more than half-way down. It has four ribs straight across, divided by 

 shallow furrows. 



The sides have three strong furrows, which at first run directly out, and then suddenly 

 bend down, expand, and nearly touch the margin. They are interlined by three others, 

 which are shallow, and cease at the straight portion. The rest of the tail is bare of ribs, 

 and apparently smooth ; but the incurved caudal fascia beneath is very broad and straight- 

 edged anteriorly. It just reaches the tip of the axis (see fig. 4). 



The metamorphosis above referred to (figs. 1, 2) is very simple. Fig. 1, a very 



