BRACHIOPODA. 349 



Lingula- iowensis.] 



Dorsal valve strongly convex, both transversely and longitudinally. In the 

 interior of this valve, the cardinal margin is broadly flattened, striated, and divided 

 centrally by a well defined, narrow depression, which terminates at a point one-fourth 

 the length of the shell from the posterior edge. Near the posterior end of this 

 depression are faint traces of the umbonal scar. The vascular trunks are discernible 

 on each side and anterior to the rostral depression, and having the same curve as 

 the outer margin of the valve, thence proceed to a point somewhat beyond the pos- 

 terior half of the shell, where they gradually converge and meet near the anterior 

 margin. Vascular branches originate only from the outer side of the vascular 

 trunks. The enclosed space seems to represent the .tracks of the anterior and 

 central muscular scars. 



The outline of this species and the convexity of the dorsal valve are variable. 

 The broadly subtriangular specimens have more strongly convex dorsal valves than 

 the narrow and less triangular form. There is no other species of Lingula from 

 Lower Silurian strata having the peculiarly deflected anterior portion of the shell 

 so characteristic of this species. Lingula linguata Hall* from the Clinton group is 

 the only other American species with this peculiarity, and differs from L, deflecta in 

 having parallel lateral margins. 



Formation and locality. From the shales near the base of the Galena group on the farm of Ole 

 Hansen, near Fountain, and in the Hudson Eiver group near Spring Valley, Minnesota. 



Collectors. E. O. Ulrich and C. Schuchert. 

 Mus. Reg. Nos. 7675, 7676. 



LINGULA IOWENSIS Oicen. 



PLATE XXIX, FIGS. 10-22. 



1844. Lingula iowensis OWEN. Geol. Rep. Iowa, Wisconsin and Illinois, p. 70, pi. xv, flg. 1. 



1851. Lingula quadrata? OWEN (not Eich.). Geological Report of Wisconsin, Iowa and Minnesota, 



pi. nB, fig. 8. 



1862. Lingula quadrata HALL. Geology of Wisconsin, vol. i, p. 46, flg. 1, and p. 435. 



1868. Lingula quadrata MKEK and WOKTIIKN. Geological Survey of Illinois, vol. iii, p. 305, pi. n, flg. 4. 



1882. Lingulella iowensis WHITFIELD. Geology of Wisconsin, vol. iv, p. 242, pi. ix, flg. 1. 



1892. Lingula iowensis HALL. Palaeontology of New York, vol. viii, part i, p. 8, pi. I, flg. 14. 



Original description: "Resembles L. lamellata H., of the Niagara group, 

 but is larger and straighter on the lateral edges. It differs from L. rectilateris 

 [probably meant L. rectilateralis Emmons], in being flatter and not so pointed at 

 the apex." 



From the figure given by Owen, we cannot be positive in the identification of 

 this species, but since comparison is made with L. rectilateralis Emmons, in the 



Pal. New York, vol. viti, p. 173, pi. ivK. fig. 5; W)2. 



