PLATE XXVII. 



Pkotolimulus Eriensis. 

 Page ia:i. 

 Kiir- 1. A view of the ventral surface from the original cast in sandstone, showing the condition of preserva- 

 tion of the different parts. 



Chemung group. LeBceuf, Eric county. Pennsylvania. 

 Fig. 2. A diagram of the same : 



cil. Cephalic doublure, 

 s. Genal spines. 



x. Hypostoiiia ('.}, or axial angulation of cephalic doublure. 

 m. Position of mouth. 

 ca. Cephalic appendages. 



f. Foliaceous terminations of the bust pair of cephalic appendages. 

 tp. Thoracic plate, 

 r. Longitudinal abdominal ridges, 

 m. Marginal abdominal spines, 

 t. Telson. 



EURYPTERUS PROMINENS. 

 Page 157. 

 Pig. 3. The cephalon, showing the prominent and anteriorly situated eyes, the ocelli, the flattened dorsal 



surface, and the oblique postero-lateral pits. 

 Fig. 4. Profile view of the same, showing the elevation of the shield, the position of the eyes ami the 

 extension of the postero-lateral angles. 



Clinton group. From the northern part, of Cayuga county. 



EURYPTERTTS BeECHERI. 



Pago 156. 

 Fig. 5. Dorsal view of the original specimen, showing the form of the body, the number, size and orna- 

 mentation of the somites, and portions of the large swimming appendages. The drawing is 

 made from a plaster cast taken from a natural mould of the dorsal surface. 

 Chemung group. Warren, Warren county, Pennsylvania. 



EURYPTERUS APPROXIMATES, 11. sp. 



Pig. 6. Dorsal view of the original, showing the cephalon and nine somites, also the conspicuous marginal 

 spines and the characteristic ornamentation of the surface. 



Waverly group. Three miles south of Warren, Warren comity, Pennsylvania. 

 This species differs from E. Pennsylvanicus, C. E. Hall, in the absence of genal spinules and con- 

 spicuous nodes on the posterior margin of the cephalon, and in the more closely appressed 

 eyes. In E. Mansfieldi. C. E. Hall, from the Coal Measures, the cephalon is longer, the eyes 

 more distant, and the abdominal segments scarcely as broad. 



