lot 



INVERTEBRATE PALAEONTOLOGY. 11)7 



mil that agree pretty nearly in outline with it, and have been thought 

 possibly 1(« belong to the same shell, though they may be entirely distinct. 

 One of these is represented by fig. 4 of the same plate, though somewhat 

 incorrectly, as the anterior muscular scar is merely narrow-ovate, and not 

 prolonged upward as in the engraving. The posterior muscular scar is also 

 wrongly represented too round, and a little too broad and low, so as to make 

 the posterior end of the pallial sinus narrower than it should be. From 

 the general form of these casts, and the nature of their muscular and pallial 

 impressions, they may possibly belong even to a species of the distinct 

 genus, Linearia. 



Nothing is known in regard to the hinge and interior of the species here 

 described, and it is only referred to the genus Tettina and subgenus Peroncea 

 provisionally from external characters. 



Locality and position. — Mouth of Judith River, from a Cretaceous bed 

 now known to hold a position at the horizon of the summit of the Fox Hills 

 group of the Upper Missouri Cretaceous series. 



T e I li n a (Pfionxa!) s c i t u I a , M. & H 



Plate 30, figs. 1, a, b. 

 Tellina seitula, Meek and Harden (185G), Proceed. Acad. Nat. Sci. Pbilad., VIII, 32. 



Shell subelliptical, compressed, thin, a little curved laterally so as to 

 make the left valve slightly more convex than the right; anterior side some- 

 what broader than the other, but rather narrowly rounded ; base nearly 

 straight, or forming a broad semi-elliptical curve; posterior side very 

 obliquely subtruncate above, subangular at the extremity below, and with a 

 moderately defined umbonal ridge in the right valve; dorsum declining 

 almost equally before and behind, from the beaks, which arc small, com- 

 pressed, and generally located slightly behind the middle ; surface ornamented 

 by fine, regular, equidistant, concentric striae ; anterior muscular impression 

 narrow-ovate, posterior broader ; pallial line distinct, and provided with a 

 nearly horizontal sinus, which extends beyond the middle of the valves, and 

 is rounded at the extremity. 



Length, 1.07 inches; height, 0.58 inch; convexity, 0.26 inch. 



This has somewhat the form of the preceding species, but is more 

 sharply rounded at the lower part of the posterior extremity, and its pallial 

 sinus is quite different from that of the casts referred doubtfully to the last; 



