Logan.] The Invertebrates, Benton Group. 457 



in the Fort Benton limestone on Salt creek, in the southern 

 part of Mitchell county. 



The species occurs associated with I. labieitus, but it is not at 

 all as abundant as the latter. 



Modiola (JBvachydontes) multilinigera Meek. Plate lxxxvi, fig. 5. 



Modiola ( Brachydontes) multilinigera Meek, 1873, Ann. Rep. U. S. Geol. 



Surv. Terr, for 1872, p. 4922; Stanton, 1892, Bull. U. S. Geol. Bur v. No.' 



106, pp. 86, 87, pi. xix, f. 3. 

 Vosella (Brachydontes ) multilinigera White, 1880, Oont. to Paleontology, 



Nos. 2-8, p. 14, pi. xn, ff. 15a, b.: Ann. Rep. U. S. Geol. Surv. Terr, for 



187S. 



Original description : " Shell rather above medium size, ob- 

 liquely arcuate subovate ; valves strongly convex along the urn- 

 bonal slopes, thence cuneate posteriorly, and abruptly curved 

 inward below the middle in front ; posterior margin forming a 

 broad, regular, convex carve, from the end»of the hinge down- 

 ward to the anterior basal extremity, which is very narrowly 

 and abruptly rounded ; anterior margin ranging obliquely back- 

 ward and downward to the narrow basal extremity, and strongly 

 sinuous along the middle, above which it projects more or less 

 beyond the umbonal ridge, so as to form a moderately promi- 

 nent, somewhat compressed protuberance ; hinged margin 

 nearly or quite straight, running at an angle of fifty to sixty de- 

 grees above an imaginary line drawn from the beaks to the most 

 prominent parts of the basal outline, and equaling about half 

 of the greatest oblique length of the valves ; beaks nearly termi- 

 nal, rather compressed, very oblique, and scarcely rising above 

 the hinge margin ; umbonal slopes prominent and more or less 

 strongly arcuate. Surface ornamented by fine lines of growth, 

 crossed by regular radiating lines that are very fine and crowded 

 on the anterior part of the valves, but become coarser above 

 and behind the -umbonal ridge, the largest being near the dorsal 

 side, where they bifurcate so as to become very fine, and curve 

 more or less upward before reaching the cardinal margin. 

 Greatest length, measuring obliquely from the beaks to the most 

 prominent part of the basal margin of a large specimen, 1.90 

 inches ; greatest breadth at right angles to the same, 1 inch ; 

 convexity, 0.76 inch." 



