4 PPP.
report of progress. c. e. beecher.
near the summit of this tubercle as in the ocelli of Eurypterus, etc. The fact that facets cannot be discerned is no criterion of their absence in the animal, for numerous trilobites and Eurypterus have as yet revealed no evidence of the compound character of their eyes, and on the other hand many species have large and distinct facets. It has also been noticed by Professor McCoy that this spot on the carapace is darker in the fossil than the general surface of the carapace, indicating the presence of pigment in the animal at this point. In the specimens of Elymocaris siliqua, Tropidocaris bicarinata and T. interrupta of the present paper this character is well marked.
 |
Explanation of Fig. 1. |
| 1. Anterior margin. | |
| 2. Furrow limiting the cephalic region. | |
| 3. Lower or ventral margin of valve. | |
| 4. Dorsal-line or hinge. | |
| 5. Posterior margin. | |
| 6. Articulating surface of somite. | |
| 7. Fimbria or setæ. | |
| 8. Crenulated inner margin of spine for the attachment of setæ. | |
| 9. Caudal plate. | |
| 10. Abdominal segments. | |
| 11. Thoracic portion of the valve extending to the furrow limiting the cephalic area. | |
| 12. Longitudinal ridge. | |
| 13. Nodes on the thoracic area. | |
| 14. Cephalic region. | |
| 15. Nodes and elevations. | |
| 16. Eye tubercles and optic spots. |
