340 THE PALEONTOLOGY^OF MINNNSOTA. 



[Lingula elder! . 



and still finer radiating lines. These give to the surface a minutely crenulated 

 appearance; also several distinct radiating lines over the anterior half of the valves 

 which interfere somewhat with the rounding of the concentric lines. 



''In the dorsal valve the impressions of the pallial sinuses [vs] are deeply 

 marked and are widely separated, leaving the area within them very considerable; 

 the central or inner ramifications [v] are very distinct, and the outer ones also for a 

 short distance from the main branches, while the posterior branches show the 

 lateral ramifications only on the outer side. The divaricator [umbonal] muscular 

 scar of the dorsal valve [g] is very large and curved forward at the sides, being sit- 

 uated well back near the apex of the valve. It cannot be positively traced on the 

 ventral side, most of the specimens being imperfect at this point. The anterior 

 adductor [anterior laterals] scars [j] are small and situated near the center of the 

 valve, while the posterior adductors [h, central scars] are large and situated outside 

 of and posterior to them so as to inclose their posterior ends. The adjuster [lateral, 

 middle and transmedian] muscles [1 i k] are distant from each other, and placed just 

 within the posterior third of the length of the shell. Two elements can be detected 

 in each scar on some individuals, but they are usually obscure. 



"On the ventral valve the lines of the pallial sinuses are nearer together on the 

 anterior half of the shell than on the dorsal, the same as shown in L. anatina, but 

 spread out rapidly toward the middle, and, on the posterior half, occupy nearly the 

 same relative position as on the other side. Near the center of the valve are seen a 

 pair of large [central] scars [h], which have advanced from behind their track, 

 forming a strong feature on the cast, as it originates just in front of the position of 

 the divaricator [umbonal] muscular scar [g], and gradually widens .as it advances 

 until it occupies fully one-half of the width of the cast near the middle of its length. 

 In the central line of these scars there is an elevated ridge, which terminates in a 

 slightly prolonged tongue, and seems to represent the central adjusters [middle 

 laterals, k]. The large scars outside of these are probably the posterior adductors 

 and external adjusters combined. Posterior to these and distant from the median 

 line are other scars, which are long and narrow, which have also left their track as 

 they have advanced. Two elements are represented on each side, and mark the 

 place of the posterior adjusters and anterior adductors [anterior, laterals and trans- 

 medians, j i]. Between the lines formed by the advance of the scars of the adjuster 

 muscles and those of the central area, on each valve, there is a narrow smooth 

 impressed space which unites with the line of the pallial sinuses at the junction of 

 the anterior and posterior branches, seen on all the specimens, and for which I have 

 not been able to satisfactorily account, as it lies within the area of the muscular 

 scar, and consequently within the walls of the perivisceral chamber. The areas of 



