PLATE XXXII. 



SILURIAN AND CARBONIFEROUS CRUSTACEA. 



Figs. 

 1 —39. Developmental stages of Trilobita (after Barrande). 



1 — 7. Agnostus bibullatus, Barr., ' Syst. Silur. de Boheme,' pi. xlix, p. 906, etage C, Skrey, Bohemia. 

 Fig. 1. Ceplialon and pygidium only observable. 



2. „ ,, and two soldered thoracic somites. 



3. „ ,, one soldered and one free. 



4. „ „ „ and two free. 



5 a, b. „ „ „ thoracic somites (form long). 



0. „ ,, ,, „ (form broad). 



7. The free thoracic segments seen enlarged. 

 8 — 14. Agnostus nudus, Beyr., ' Barr. Syst. Silur. de Boheme,' pi. xlix, p. 903, etage C, Skrey, Bohemia. 

 Fig. 8. Ceplialon and pygidium only observable. 



9. ,, ,, and two soldered thoracic somites. 



10. „ „ and one soldered and one free thoracic somites. 



11. „ „ and two free thoracic somites. 



12 a, b. „ „ ,, „ (form long). 



13. „ „ „ ,, (form broad). 



14. The two free thoracic somites seen enlarged. 



15 — 28. Sao hirsuta, Barr., ' Syst. Silur. de Boheme,' pi. vii, etage C, Skrey, Bohemia. 



Figs. 15 and 16. Two individuals in which there is no line of separation between the head and the pygidium ; in 

 Fig. 15 a slight indication on the axis marks the commencement of the division of the 

 body into somites ; the glabella is also marked by a simple fold on the cephalic portion. 

 Fig. 17. Shows the second stage with three soldered somites; the thorax is indicated (form broad). 



18. The third stage. The genal spines and the points of the pleurae are well seen; four to five 



soldered somites are indicated. 



19. Fifth stage. Thorax longer than head, with three free and three soldered somites (form broad). 



20. The same degree of development as Fig. 19 (form long). 



21. Broad form, with four free segments and three or four soldered segments. 



22. Tenth stage. Form broad ; eight free and three soldered segments ; the compound eyes are seen 



at this stage. 



23. Twelfth stage. Form broad ; ten free and three to four soldered somites ; the eyes and ornament 



on the head are seen. 



24. Fourteenth stage. Form long; twelve free and two to four soldered somites; four lobes marked 



on glabella. 



25. Sixteenth stage. Form long ; fourteen free and three soldered somites. 



26. Eighteenth stage. Form long; sixteen free and three soldered somites; the number of somites is 



completed at this stage. 



27. Twentieth stage. Form long; all the segments of the thorax and pygidium are very distinct; 



seventeen free somites and two soldered. The ornamentation at this stage assumes all the 

 characters of the adult. 



28. View in profile, restored from numerous fragments, showing all the ornamentation of the test. 



(P. 223.) 

 29 — 39. Trinucleus ornatus, Sternb., ' Barr. Syst. Silur. de Boheme,' pi. xxx, p. 624, etage D, Trubin. 

 Fig. 29. Young, with no thoracic segments, and without genal spines. 



30. „ „ „ and with „ 



31. „ one „ without ,, 



32. „ „ „ and with „ 



33. „ two „ without „ 



34. „ „ „ and with „ 



35. „ three „ „ „ 



36. „ four „ „ ,, 



37. „ five „ without „ 



38. Adult, one part of the test on the right genal border preserved. 



39. „ head-shield without genal spines. 



40. Trinucleus ornatus, Sternb., 1833. Hypothetical development of the fringe of glabella, after Salter. 



41. Fringe of Trinucleus fimbriatus, Murch., 1839. 



Figs. 40 and 41 illustrate Mr. Salter's paper, ' Quart. Journ. Geol. Soc.,' 1847 (vol. iii, p. 252, woodcuts). (P. 218.) 



42. Cyclus Rankini, H. Woodw., 1868. (P. 254.) Coal-shales, Carluke, Scotland (diameter 4 lines). 



43. — radialis, Phillips, sp., 1829. (P. 253.) Carboniferous Limestone, Settle and Bolland, Yorkshire. 



a, dorsal aspect ; b, side-view. 



44. — Ilarknessi, H. Woodw., 1870. (P. 252.) Carboniferous Limestone, Little Island, Cork, Ireland. 



a, dorsal aspect ; b, side-view. 

 45 — bilobatus, H. Woodw., 1870. (P. 249.) Carboniferous Limestone, Settle, Yorkshire. 



a, dorsal aspect ; b, side-view. 



46. — Jonesianus, H. Woodw., 1870 (P. 254) (magnified four times). Carboniferous Limestone, Little Island, Cork, Ireland. 



a, dorsal aspect ; b, side-view. 



47. — Wrightii, H. Woodw., 1870. (P. 251.) Carboniferous Limestone, Little Island, Cork, Ireland. 



a, dorsal aspect ; b, side-view. 



48. — {Halicyne) lawns, H. von Meyer, sp. (P. 255.) Muschelkalk, Rottweil, Germany. 



a, dorsal aspect ; b, side-view. 



49. — (Halicyne) agnotus, H. von Meyer, sp. (P. 255.) Muschelkalk, Rottweil, Germany. 



a, dorsal aspect; b, side-view. 



