Clark. — Trenton Limestone at Martinsburg. 



EXPLANATION OF THE PLATE. 



Fig. 1-3. TripJecia cuspidata (Hall). Posterior, lateral, and anterior views 

 of a specimen of average size from the base of the Trenton at 

 Martinsburg. Natural size. 



Fig. 4-6. The same species, from the same locality. Anterior views of 

 three specimens to show variation in shape of sinus, with per- 

 sistence of the central groove. Natural size. 



Fig. 7-9. Triplecia schucherii Clark. Posterior, lateral, and anterior views 

 of the holotype, a large specimen from the base of Trenton at 

 Martinsburg. Natural size. 



Fig. 10, 11. The same species, from the same locality. Posterior and ante- 

 rior views of a specimen with a very high narrow fold, but a 

 flat-bottomed sinus. Natural size. 



Fig. 12. The same species from the same locality. A smaller specimen 

 with a low rounded fold, and a flat-bottomed sinus. Natural 

 size. 



Fig. 13-15. Triplecia extans (Emmons) . Posterior, lateral, and anterior views 

 to show the high fold with the evenly rounded sinus. Natural 

 size. 



Fig. 16. Phragmclites compressus Conrad. A photograph of a specimen from 

 the base of the Trenton at Martinsburg. Natural size. 



Fig. 17. Cheirocrinus anatiformis (Hall). A photograph of two fragmentary 

 specimens from the upper part of the Trenton at Martinsburg, 

 to show the pectinirhombs. Natural size. 



Fig. 18. Carneyella raymondi Clark. A photograph of the type, resting 

 on the anterior part of the pedicle valve of a Rafinesquina. 

 From the base of the Upper Trenton at Martinsburg. Twice 

 natural size. 



Fig. 19. The same specimen. An enlarged drawing. 4.5 times natural size. 



