PLATE V. 



Page. 

 Fi(i. 1. Productus nebraskensis 370 



A small, well-preserved, and very characteristic specimen belonging to this species. 



Dorsal view. 



Hermosa formation: Hermosa Creek, Durango quadrangle (station 2239). 



Figs. 2 and 2a. Productus nebraskensis 370 



Another somewhat larger but imperfectly preserved example. 

 Fig. 2. Ventral view. 



2a. Side view. 

 Hermosa formation: Hermosa Creek, Durango quadrangle (station 2239). 



Fig. 3. Productus sp. a 372 



A very imperfect ventral valve, which shows the irregular and interrupted character of 

 the striae, and in some cases the scars left by the bases of small spines which have been 

 broken off. 

 Specimen seen from above. The restored outline is wholly hypothetical, as no specimen 



has been seen which was entire. 

 Hermosa formation: Animas River, Durango quadrangle (station 2335). 



Figs. 4 and 4a. Marginifera lasallbnsis? 372 



The interior of a dorsal valve. 



Fig. 4. Posterior view. The figure represents the specimen as somewhat less symmetrical 

 than it really is. 

 4a. Side view of the same. 

 Weber formation: Gulch near Double Top, Crested Butte quadrangle (station 2316) 



Figs. 5 to 5b. Marginifera muricata 373 



A specimen of the coarsely ribbed variety, considerably exfoliated. 

 Fig. 5. Specimen seen from above. 

 5a. Side view. 

 5b. Anterior view. 

 Maroon formation; Cement Creek, Crested Butte quadrangle (station 231S). 



FiGS. 6 to 6b. Marginifera muricata 373 



Another example of the common type similar to the last. This is the specimen figured by 



White in 1877. The present figures are to a certain extent enlargements. 

 Fig. 6. Specimens seen from above. 

 6a. Side view. 

 6b. Posterior view. 

 Maroon formation; Near the head of Eock Creek, Elk Mountain region (station 2244). 

 496 



