BRACHIOPODA. 339 



Lingula elder!.] 



produced by a single pair of muscles extending across the ante-lateral region of the 

 visceral area, and by the contraction of these, the valves are closed. The transmedian 

 impressions, are made by a triple muscle, one band of which is on one side of the 

 visceral area, the other two on the other side, the two lateral components crossing 

 each other in passing from the posterior region of the pedicle-valve to the medio- 

 lateral region of the opposite valve. By the action of these muscles the animal is 

 able to slide apart the anterior and .posterior extremities of its valves. The mus- 

 cular region in each valve is surrounded by the parietal bands, which leave more or 

 less distinct impressions upon the shell. 



"The anterior internal surface of each valve bears traces of two strong pallial 

 sinuses, which nearly meet in the axial line before reaching the anterior margin. 

 In front and behind are radiating vascular markings. 



" Shell substance composed of alternating lamellae of chitinous and calcareous 

 material. 



" Type Lingula anatina Lamarck." (Hall, op. cit.) 



Species of this genus had their origin in the St. Croix formation,* and thence 

 lived through all geologic times. Several species are still living, usually in shallow 

 water, of which L. anatina, the type of the genus, is the most abundant and widely 

 distributed. 



LINGULA ELDEBI Whitfield. 



PLATE XXIX. FIGS. 1-4 



1875-77. Lingula quadrata WINCHELL (non EICHWALD). Fourth Annual Report of the Geological " 



and Natural History Survey of Minnesota, p. 49. 



1880, June. Lingula elderi WHITFIELD. American Journal of Science, third ser., vol. xix, p. 472, 



flgs. 1, 2. 



1880, July. Lingula minnesolensis N. H. WINCHELL. Eighth Annual Report of the Geol. and 



Natural History Survey of Minnesota, p. 61. 



1882. Lingula elderi WHITFIELD. Geology of Wisconsin, vol. iv, p. 345, pi. xxvii, flgs. 1-5. 



1392. Lingula elderi HALL. Palaeontology of New York, vol. viii, pt. i, p. 11, pi. L, flgs. 21, 22. 



Original description. " Shell oblong and subquadrangular in outline, with nearly 

 or quite parallel lateral margins, which are but very slightly curved; anterior and 

 posterior extremities subequal, the upper end being slightly angular at the apex and 

 on the shoulders, while the front or posterior end is broadly rounded. Valves 

 rather strongly convex, the dorsal or shorter valve being a little the more convex 

 and the valve, as shown by the cast, frequently marked by a slight flattening, or 

 even by a depressed longitudinal line along the middle of the front half." Surface 

 of the shell nearly smooth and glossy, marked by fine concentric lines of growth 



* This statement is based 'largely on professor James Hall's late investigations as given on p. 6. Paleontology of New 

 York, vol. vlii. 1892. 



