Key: {253} A Prosomatic. B Mesosomatic. C.c. Coelomic cavities. ---------------------------------------------------------+--------------- LIMULUS. | VERTEBRATE. ---------+----------------+-----------------------+------+--------------- Segments.| Appendages. | Eurypterid appendages.| C.c. | Coelomic | | | | cavities. ---+-----+----------------+-----------------------+------+--------------- | 1 | Cheliceræ or | Cheliceræ | 1 | Anterior | | 1st locomotor.| | | | 2 | 2nd locomotor |} | | A | 3 | 3rd " |} Endognaths | 2 | Premandibular | 4 | 4th " |} | | | 5 | 5th " |} | | | 6 | 6th " | Ectognath | 3 |} Mandibular | 7 | Chilaria | Metastoma | 4 |} ---+-----+----------------+-----------------------+------+--------------- | 8 | Operculum |} Operculum (Genital) | 5 |} Hyoid | 9 | 1st branchial |} " (1st branchial) | 6 |} | 10 | 2nd " | 2nd branchial | 7 | 1st branchial B | 11 | 3rd " | 3rd " | 8 | 2nd " | 12 | 4th " | 4th " | 9 | 3rd " | 13 | 5th " | 5th " | 10 | 4th " | 14 | 6th " | | 11 | ---+-----+----------------+-----------------------+------+---------------