PLATE III 

 LARVAL STAGES OF TRILOBITES (PAGES 171-173) 



FIGURE 1. Solenopleura Robbi Hartt. (After Matthew.) Anapro- 

 taspis stage; showing obscurely annulated axis. X 30. St. John Group, 

 Cambrian, New Brunswick. 



FIGURE 2. Liostracus onangondianus Hartt. (After Matthew.) 

 Anaprotaspis stage; the neck lobe is the only one distinctly marked. 

 X 23. Cambrian, New Brunswick. 



FiGURE3. Ptychoparia Linnarssoni Walcott. (After Matthew.) 

 Anaprotaspis stage; axis slender, slightly annulated; pygidium defined 

 by transverse furrow. X 30. Cambrian, New Brunswick. 



FIGURE 4. Ptychoparia Linnarssoni, Walcott. (After Matthew.) 

 Protaspis ; representing a later moult than the preceding, and showing 

 stronger annulations on the axis, with an additional one on the pygidium. 

 X 25. Cambrian, New Brunswick. 



FIGURE 5. Ptychoparia Kingi Meek. Anaprotaspis or early stage ; 

 showing obscurely defined characters, partly due to the fact that the 

 specimen is a cast. X 45. Cambrian, Nevada. 



FIGURE 6. Ptychoparia Kingi Meek. A later stage (metaprotaspis) ; 

 showing the strongly annulated axis, the eye-line, the free-cheeks includ- 

 ing the genal angles, and two segments on the pygidium. X 45. Cam- 

 brian, Nevada. 



FIGURE 7. Ptychoparia Kingi Meek. (After Walcott.) An adult 

 specimen. This and the other figures of adult individuals are represented 

 in outline, with the free-cheeks shaded, to bring out more strongly the 

 changes in the structure of the cephalon. X J. Cambrian, Utah. 



FIGURES. Sao hirsuta Barrande. (After Barrande.) Anaprotaspis 

 stage; showing obscurely the limits of the pygidium, the eye-line, and 

 the nearly cylindrical glabellar axis expanding on the frontal margin. 

 This and the two following specimens are preserved as casts. X 30. 

 Cambrian, Bohemia. 



FIGURE 9. Sao hirsuta Barrande. (After Barrande.) A later moult, 

 probably near the end of the metaprotaspis stage ; showing the annulated 

 axis expanded in front; free-cheeks narrow and marginal ; pygidium 

 of four segments, with pleura distinctly marked and grooved. X 30. 

 Cambrian, Bohemia. 



FIGURE 10. Sao hirsuta Barrande. (After Barrande.) A more ad- 

 vanced stage at or after the close of the paraprotaspis, in which the 

 pygidium is complete, but before the first free thoracic segment is de- 

 veloped. X 30. Cambrian, Bohemia. 



FIGURE 11. Sao hirsuta Barrande. An adult individual combining 

 the characters as shown in several of Barrande's figures of this species. 

 X A. Cambrian, Bohemia. 



FIGURE 12. Triarthrus Becki Green. Anaprotaspis; showing the 

 annulated axis, terminating before reaching the anterior margin ; the 

 eye-lines extending from the first segment to the marginal eye-lobes ; 

 pygidium defined by a slight groove, and including two segments of the 

 axis. X 45. Ordovician, Utica Slate, near Rome, New York. 



FIGURE 13. Triarthrus Becki Green. Protaspis at a later moult ; 

 showing slight increase in size and the addition of a segment to the 

 pygidium. X 45. Ordovician, Utica Slate, near Rome, New York. 



FIGURE 14. Triarthrus Becki Green. An adult individual of this 

 species. X Ordovician, Utica Slate, near Rome, New York. 



