No. 89.] 



115 



the two others. The pygidium has four or five rings on the axis, and the laterla 

 lobes are expanded and the extremity rounded; moreover I am able to count but 

 eleven articulations in the thorax : these, with other characters enumerated, seem 

 to exclude it from generic association with the two species referred to Olexus. 

 For these, excluding the one referred to Peltura, I would propose the generic de- 

 signation BAjRRAXDIA. 



GENUS BARRANDIA*(n.g.). 



Gexeral form broadly ovate or elongate ovate, distinctly trilobate. Cephalic shield 

 broad, somewhat semicircular; the width more or less than twice the length, 

 with the posterior angles projecting in long spiniform points : the posterior 

 margin is nearly straight or sligTitly concave, with a slight sinuosity at the 

 outer angle just within the cephalic limb; the anterior and lateral margins have 

 a thickened or elevated border, within which is a well marked groove or de- 

 pression of the crust. The glabella is well pronounced, of nearly equal width 

 throughout, or slightly narrowing and rounded in front; marked by three pairs 

 of furrows (perhaps from two to four), the posterior one of which is nearly or 

 quite continuous across from the posterior angles of the eyes. The facial suture 

 has not been fully determined, but appears to extend in a curving line from the 

 front margin to the anterior angle of the eye, and from the posterior angle of the 

 eye it turns abruptly outwards towards the postero-lateral angle of the cephalic 

 shield. 



Eyes large and well developed, elongate semilunate, extending from near the base 

 of the shield more than halfway to the anterior margin. Hypostoma broadly- 

 ovate, little longer than wide. 



Thorax composed of thirteen or fourteen articulations; the axis being moderately 

 convex, and usually much narrower than the lateral lobes (and sometimes ap* 

 parently marked by a row of nodes or short spines along the summit). Lateral 

 lobes nearly flat; the ribs, to about the eighth or ninth, extending almost rec- 

 tangularly, or slightly inclined from the axis for one-third to one-half their 

 length, where they are bent abruptly backwards. The third segment is stronger, 

 and much more prolorfged than the others. The last segments of the lateral lobes 

 are produced directly backwards, or sometimes a little convergent below. The 

 segments of the lateral lobes are marked by a broad longitudinal furrow nearly 

 parallel to the anterior margin; leaving an abruptly elevated ridge or border 

 upon that side as far as the geniculation of the segment, where the groove runs 

 along the centre, dying out on the recurved extremities. 



Pygidium distinct, narrow, elongated, the axis narrow and acutely pointed; without 

 rings ? Lateral lobes narrow or obsolete, and free from transverse ridges or fur- 

 rows. 



The accompanying figure, illustrating this gemis, combines characters observed 

 in several imperfect specimens of the same species. The form of the cephalic shield 

 is shown in two or three individuals : the glabella is crushed in all the specimens 

 examined; but the form is made out, as nearly as possible, from the materials in 



* In honor of M. J. Barrande, author of Systme Silurien de Boh'me. I can ^y regret 

 that I have not something of greater importance to offer as a tribute to the name, aM in com- 

 memoration of the rare merits and eminent services in the cause of science, of this distinguished 

 palaeontologist. I believe, however, that these form3 will hereafter be found to mark an impor- 

 tant horizon in our geological series ; associated as they are with other forms that indicate the 

 ast appearance and final dying out of the types of that ancient crustacean fauna, TyLich 

 marked, so far as we now know, the dawn of life upon our planet. 



