PLATE IV 

 LARVAL STAGES Oi' TRILOBITES (Pages 173-17(i) 



Figure 1. — Acidaspis tuhereulala Conrad. Anaprotaspis ; showing 

 denticulate margin and spines on cephalon; axis strongly annulated ; 

 eyes sub-marginal. X 20. Lower Helderberg, Albany county, New York. 



FiGDRE 2. — The same ; profile, slightly oblique. X 20. 



Figure 3. — Acidaspis iuherculata Conrad. An adult individual, re- 

 stored from fragments and an entire enrolled specimen. Natural size. 

 Lower Helderberg, Albany county. New York. 



Figure 4. — Arges consangiiineus daAs. Dorsal view of a larva at 

 or after the close of the paraprotaspls stage ; showing the form and orna- 

 mentation. X 20. Lower Helderberg, Albany county. New York. 



Figure 5. — Proelus parriusculus Hall. Anaprotaspis; showing 

 strongly annulated axis, with groove at each side; large prominent 

 anterioi' eyes ; pygidial pleura indicated by faint grooves, x 45. Ordo- 

 vician, Utica Slate, near Rome, New York. 



Figure 6. — Proiitus parviusculus Hall. A later moult, near the close 

 of the paraprotaspls stage ; showing the larger pygidium which, how- 

 ever, is still incomplete, and the slight backward movement of the eyes. 

 The right side of the specimen is restored, x 4.5. Ordovician, Utica 

 Slate, near Rome, New York. 



Figure 7. — Proelus parviusculus Hall. An adult individual. X 2. 

 Ordovician, Utica Slate, near Rome, New I'ork. 



Figure 8. — Dalmanites socialis Barmnde. (After ISarrande.) Ana- 

 protaspis stage; showing the large strongly annulated axis; the prom- 

 inent anterior marginal eyes ; mucronate genal angles ; pygidium of 

 three segments. X 30. Ordovician, Bohemia. 



Figure 9. — Dcdmanites socialis Burvande. (After Barrande.) IMeta- 

 protaspis stage ; showing the stronger definition of the pleura of the 

 pygidium. X 30. Ordovician, Bohemia. 



Figure 10. — Dahnaniles socialis Barrande. (After Barrande.) The 

 specimen probably represents the close of the paraprotaspls stage, and 

 shows four segments in the pygidium and the first evidence of the 

 backward movement of the eyes, which now indent the margin. X 30. 

 Ordovician, Bohemia. 



Figure 11. — Da^manito .wciaZis Barrande. (After Barrande.) Out- 

 line of an adult individual. X \. Ord(jvician, Bohemia. 



