AND DISTRIBUTION OF TRILOBITES, 275 
bella somewhat narrow anteriorly. Eyes concave. Maxillary 
shields generally detached, horned. Thorax 15(?)-jointed. 
Fins longer than the breadth of the axis, acute. Caudal 
shield with an articulated axis and ribbed sides, frequently 
dentated at the margin. Aluminiferous clay of the North. 
P. gibbosus, Dalm., latus, Boeck, &c. 
Family IV. Odontopleure.—Facial suture terminating at the 
posterior margin more or less distant from the angles of the ce- 
phalic shield. Eyes smooth. Glabella narrow anteriorly, divided 
into lobes at the sides. Margin of the cephalic shield dentated. 
Thorax 8-, 9-jointed and upwards. Caudal shield considerably 
smaller than the cephalic shield, with longer or shorter spiny 
appendages. The fins of the thorax are likewise frequently elon- 
gated into spines. 
Although the forms which we have here arranged together 
correspond very much in habit, and possess distinguishing cha- 
racters from others, the appearance of a perfectly analogous form 
among the species of Phacops (Ph. arachnoideus, Goldf.) is ne- 
vertheless very remarkable. 
XVIII. Odontopleura, m. (6500s, the tooth; wrevpa, the rid). 
Glabella semicircular. Facial suture, see above. Eyes 
‘smooth. Body 9-jointed, | Caudal shield furnished with a 
2-jointed axis and dentated or spiny margin. 
1. O. bispinosa,m. (PI. 1V. fig.12.) (ovata,m. Dissert. inaug.) 
Fins elongated into two long spines.— Northern drift: Upper 
Silesia. 2. O. mutica,m. Semi-contractile. Fins scarcely 
pointed at their extremity. Cephalic and caudal shield 
coarsely serrated.—From the same locality. 3. QO. crenata, 
m. Contractile. Margin of the cephalic shield curved.— 
Gothland. 4. O. centrina (Cal.), Dalm. 5. O. dentata, 
Goldf. 
XIX. Arges. Eyes? Facial suture straight posteriorly. Cheeks ? 
Body 8-jointed. Caudal shield with an indistinct 4-jointed 
axis. All the fins are serrated. 
Family V. Trinuclei—Head with a broad even reticulate 
foveolate margin, which is lengthened into horns posteriorly. 
Surface of the thorax horizontal, only curved downwards with 
the apex. Facial suture terminating at the posterior margin. 
Kyes generally unknown. 
