Contributions to Palceontology. 



101 



LINGULA AMPLA. 



PLATE I. FIG. 10. 



Lingula ampla : Owen, Geol. Report on "Wisconsin, 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 contour of the shell, and formed more 

 " after the beaks of Terebratula. A few faint concen- 

 " trie strise. Length \^ of an inch, width 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 elsewhere in Wisconsin." 



In the lower beds at Trempaleau there occurs a large Lingula, 

 which, in its greatest dimensions, is about by -J-]- of an inch : a 

 specimen of this species is represented on Plate 2, 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 Wisconsin " may have been a species of similar form and size 

 from the higher beds of the formation. 



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. 



