PLATE 31 



Spirifer plicatus (Weller) 



Page 181 



I— 13 Various views of silica replacements of this species, 9 and 13 natural 

 size, all the rest x i^, showing the usual expression, contour, 

 mode and degree of plication of the valves 

 14 A ventral valve with median plication in the sinus, a less common 

 feature than the low sinus on the fold of the dorsal valve, x i^ 

 {see fig. 7, II, 13] 

 15, 16 Exterior and interior of a dorsal valve, x i^ 



Grande Greve limestone. Grande Greve 

 17 Exterior of a dorsal valve with sulcate median fold and well developed 

 concentric striae, x ij^ 

 Grande Greve limestone. Perce Rock 



This shell is far more abundant at Perce than on the Forillon, but the 

 preservation at the former locality is less favorable for illustration of 

 the species 



Spirifer modestus Hall var. nitidulus no v. 



Page 182 



18-20 Three views of a silica replacement, x 5 

 21-23 A similar replacement, x 3 



24 Interior of dorsal valve, x 5 



Grande Grtve limestone. Grande Greve 



Cyrtina rostrata Hall 



(=C. affinis Billings) 



Page 183 



25 Interior of dorsal valve, x 3 



26-27 Posterior and anterior views of ventral valve 



28 A younger and sparsely ribbed ventral valve, x 2. All are silica 

 replacements 

 Grande Greve limestone. Grande Greve 



