2 PALEONTOLOGY OP THE UPPER MISSOURI. 



would remark, however, that we have had an opportunity to examine a collection 

 of the typical species from the falls of St. Croix, recently deposited in the museum 

 of the Smithsonian Institution, and that we have seen the peculiar visceral scar 

 shown in the form supposed to be the smaller or dorsal valve of the same. The 

 specimens of the other valve, we have seen, are not in a condition to show so clearly 

 the trilobate visceral scar, though a few of them exhibit traces of its outline. 

 From the examination of these specimens, and the published figures, we are clearly 

 satisfied that these internal markings are the scars of the visceral sack, and not, as 

 has been supposed, " muscular impressions." The impressions of the posterior 

 occlusor muscles are located much as in Lingula, one on each side of the middle 

 lobe of the visceral scar, in the sinus between it and the lateral lobe on each side. 1 

 In the other valve the minute impressions -of these muscles are placed apparently 

 within the middle lobe of the flabelliform visceral scar, much as in Lingula, except- 

 ing that they are closer together, and located a little farther back. 



It will thus be seen that the arrangement of the muscular system in this ancient 

 type has yet to be clearly defined, and that it is much more nearly related to the 

 genus Lingula than has been supposed ; though the differences in the nature of the 

 visceral scars, and the general form of the shell, were probably coincident with 

 differences in the structure of the animal that would place this type in a distinct 

 genus from our modern Lingulas. 



The only species yet positively known to possess the characters of this genus, is 

 from the base of the Silurian System, though it is probable many possibly all 

 of the older Palaeozoic species usually referred to the genus Lingula, will be found 

 to belong here. Until the interior of many species have been examined, nothing 

 can be known in regard to the geological range of the genus. So far, however, as 

 can be determined from external form alone, it seems to range up at least to the 

 Medina Sandstone of N. York Upper Silurian Series Lingula cuneata of Conrad, 

 from that rock, having more nearly the outline of the typical species of this genus 

 than that of the modern Lingulas. 



langnlepis pinniformis. 



(PLATE I, Fig. 1, a, 6.) 

 Lingula antiqva, HALL, Foster & Whitney's Report Lake Superior, 1851, p. 204, pi. xxiii, Fig. 2. MEEK & HATDEN, 



Proceed. Acad. Nat. Sci. Phila., March, 1858, p. 49 (not HALL, 1847). 



Lingula pinniformis, OWEN, Rept. Geol. Wisconsin, Iowa, and Minnesota, 1852, pi. i, B, Figs. 4, 6, 8, &c. 

 Lingulepis pinniformis, HALL, Sixteenth Report Regents' University, N. Y., 1863, p. 129, pi. vi, Figs. 14 and 16. 



Shell subovate, or ovate-subtrigonal, rounded in front and angular at the beaks, moderately convex ; sides con- 

 verging to the beaks, with straight or concave outlines. Beaks more or less produced, that of the larger valve 

 attenuate and acutely pointed. Surface marked by rather obscure concentric strise, which are sometimes crossed by 

 faint radiating lines, usually moat apparent on exfoliated surfaces, and generally quite distinct near the front, on 

 the interior surface, and on internal casts. 



Length, 0.68 inch ; breadth, 0.50 inch. Other individuals in the collection proportionally wider. 



This shell agrees so nearly in outline with the Escanaba form figured by Prof. 



1 On comparing the trilobate visceral scar of the larger valve in Lingulepis, with that of the same 

 valve in the recent Lingula analina, as figured by Mr. Davidson (Mon. Carb. Brach. Grt. Brt., p. 

 200), it will be seen that they are very similar, excepting in the greater prolongation of the lateral 

 lobes in Lingulepis. 



