CONTRIBUTIONS TO PALiEONTOLOGY. 125 



BUACHIOPODA. 



GENUS LINGULA* ( Bruguiere). 

 LINGULA AMPLA. 



PLATE VI. FIG. 10. 



Lingula ampla : Owen, Geol. Report on Wiseonsin, Iowa and Minnesota, p. 583, 



Tab. 1 B, f. 5. 



Dr. Owen describes this species as having the following characters : 



"A greater circumference and superficial area than any of the 

 " others hitherto discovered, in F 1. Shell nearly oval, rather 

 " flat : beak blunt and not projecting beyond the general con- 

 " tour of the shell, and formed more after the beaks of Tere- 

 " BRATULA. A few faint concentric striae. Length ii of an inch ; 

 " width y\ of an inch.'' 



The species is cited from " the Obolus grits, member c, near 

 Mountain island " ; and " at the Dalles of the St.Croix, and else- 

 " where in Wisconsin". 



In the lower beds at Trempeleau there occurs a large Lingula, which, 

 in its greatest dimensions, is about -f^ by ^^ of an inch : a specimen of this 

 species is represented on Plate 7, fig. 22. Since this is the only one known 

 to me in these lower beds, from which L. ampla has been cited by Dr. 

 Owen, I am forced to regard it as the typical form of the species. 



The shell is rather flat, compared with its size, but not so flat as a species 

 in the higher beds. In well preserved specimens, the lamellose concentric 

 striae are well defined, but I have not observed any radiating striae : the 

 cardinal slopes are nearly straight for more than one-third the length ; the 

 beak is robust and obtuse [the figure represents the beak too acute]. 



This species is quite distinct from any of those in my collection from 

 St.Croix river, and I can scarcely suppose it occurs in that position. Its 

 citation thence by Dr. Owen has probably arisen from some admixture of 

 specimens. The specimens from "elsewhere in Winconsin" may have been 

 a species of similar form and size from the higher beds of the formation. 



This Lingula characterizes the lowest fossilifcrous beds of the formation 

 on the Upper Mississippi river near Trempaleau, and opposite the mouth 

 of Black river. 



* The Genus Lingula has been recognized in the lower rocks, from its similarity 

 of external form and texture to the recent Lingula. It may he doubtful whether the 

 internal structure and arrangement of muscular impressions has been determined in 

 any one of these, and it will probably be a long time before this will be done for any 

 large number of the species. Recent examinations lead me to doubt, much against my 

 inclination to disturb the generally received opinion, whether any of these older forms 

 belong to Lingula proper. 



