16g jurassic peeioi). 



Family PTEREIDJE. 



Genus INOCERAMOS Sowerby, 1814. 



Inoceramus crassalatus White. 

 Plate XIII, fig. 4 a, h, and c. 



Shell rather small, thin; valves subequal, moderately convex, subo- 

 vate or obscurely tetrahedi'al in marginal outline; hinge-line rather short, 

 forming an angle with the axis of the shell of about seventy degrees ; 

 beaks small, not very prominent. Left valve more capacious than the right, 

 having an indistinct aiu'icular furrow extending from just beliind the beak 

 to the postero-basal border, obscurely defining a thick posterior wing ; but 

 the right valve has little or no trace of a similar furrow. 



Surface of both valves marked by the usual lines of growth, and also 

 by more or less numerous, slightly-raised, concentric folds. 



Greatest length of an average example in the collection, about thirty 

 millimeters; thickness, both valves together, about fifteen millimeters. 



Position and locality. — Strata of the Jurassic period ; North Fork of 

 Virgin River, Utah. 



Order DIMYAMA. 

 Family TRIGONIID^. 



Genus MYOPHORIA Bronn, 1830. 



Myophoria ambilineata White. 

 • ■ Plate XIII, fig. 5 a and 6. 



Shell subcircular or obscurely four-sided in outline, being very slightly 

 longer than high, moderately gibbous ; base broadly rounded ; front regu- 

 larly, but more shortly, rounded than the base ; hinge-line of moderate 

 length, straight or nearly so ; posterior border, from the extremity of the 

 hinge-line to the infero-posterior. angle, nearly straight or slightly convex ; 

 infero-posterior angle sharply rounded; umbonal ridge passing to it from 

 the beak with a slight curve, the convexity of Avhich is toward the front ; 

 that ridge sometimes forming a slightly-raised but distinct carina. 



Surface, both in front of and bcfhind, the umbonal ridge marked by 



