OF THE SPECIES. 93 



form of a triangular lobe ; the third of a narrow transverse protuberance, the margin of 

 articulation exceeding it in point of width. The eyes are enormously large, and occupy 

 the entire sides of the cephalic shield from the anterior to the posterior margin. There are 

 eleven body rings. 



Caudal shield oblong, trilateral, rather narrow, the axis furnished with seven distinct 

 rings, the sides with six short ribs, and the extremity acutely angular. 



Remark. — According to the researches of Römer {d. Rhein, uhergamjsgel , 83. G9. 2), this species 

 possesses not merely elongated cephalic angles, but also dentations to the caudal shield, and belongs 

 therefore to the last group, called by Milne Edwards Pleur acanthus. I have therefore indicated tlie 

 ceph.alic angles and caudal points according to Romei-'s drawing in the former figure, which represented 

 mere impressions in stone. Römer calls it Pleur. laciniatus. 



9. Ph. proeevtts : Tuberculo capitis antico rhombeo, secundo et tertio sensim minoribus, hoc a 

 spire articulatoria, longius distante ; rhachi caudali 8 annulata, costis lateralibus septem. Long. 2". 

 Table IV, Fig. 3. 



Be/.—EuMR. Dissert. 25. 14. 



Loc. — The Bohemian grauwacke of Ginec. 



Comparatively shorter and broader than the preceding species ; the anterior lobe of 

 the glabella forming a highly convex, granulated, oblique, rhombic plate, to which the 

 second wedge-shaped lobe is as closely joined as the third and narrower one, which is 

 contracted laterally, is to this. The margin of articulation then follows posteriorly at a 

 somewhat greater distance. 



The eyes not large in proportion. They correspond entirely to the second lobe of the 

 head, beyond which they do not project at all anteriorly, and but little posteriorly. I have 

 not seen the body. The caudal shield is trilateral, heart-shaped, convex, pointed at the 

 end, and has eight rings, successively becoming narrower, besides an ovate terminating 

 joint ; seven broad ribs, rather impressed longitudinally, are visible on the sides. The 

 smaller anterior margin of articulation has been left out in this calculation ; if we count it 

 likewise, it would increase the number of rings, including the terminal joint, to ten. 



Remark.- — I have recently had opportunities of examining many specimens from the ^Mineralo- 

 gical ^Museum of the University of Halle. In many of them there are distinct traces of long processes 

 on the cephalic shield, and of a spine at the extremity of the caudal shield, which suggests the idea 

 that Phacops proavus may perhaps be identical with Ph. mucronatus. 



Siih-(/roup (c). The caudal shield is pointed at the extremity, and has no lateral spines. 



10. Ph. Hausmanni : Oculis maximis, usque ad limbum scuti cephulici cxtensis ; rhachi candie 

 19-20 annulata, costis latei'alibus 15. Long. 3-5". 



Re/. — Jsaj)/i. Hausmaimi, Broügü. Cr. Joss. 21. 3, PI. II, Fig. 3, A, B. Schloth. 

 Naclitr. ii,20. 35, Tab. XXII, Fig. 7. Sternb. VerhancU. 1825, 77, Tab. II, Fig. 

 3, A-C. Dalm. Palcead. GG. 4. Phac. Hausmanni, Emmr. Dissert. 24. 13. 

 Loc. — The gray transition limestone of Bohemia, on the left shore of the Beraun, near 

 Karlstein, and at the shores of the Moldau, near Kosorz and Brauik. 



The largest species of the genus, and particularly distinguished by its very large eyes, 

 the lenses of which, however, are remarkably small. The glabella is shorter and broader 



