194 NORTH AMERICAN INDEX FOSSILS. 



VIII. Leptobolus Hall. 

 Minute, with convex valves. Pedicle valve with cardinal area cut 

 by a pedicle groove. Brachial valve slightly thickened on cardinal 

 margin. Interior of both valves with two or three diverging septa. 

 Ordovicic. 



15. L. insignis Hall. Ordovicic. 

 Orbicular with a scarcely pointed beak. Valves regularly con- 

 vex when not compressed. Specimens usually found flattened. 

 Surface marked by concentric growth lines. Differs from L. occi- 

 dentals in being more nearly circular, with a shorter beak and more 

 regularly convex valves. 



Utica of New York, Ohio, Ontario. 



16. L. occidentalis Hall. Ordovicic. 

 Widest below the middle. Valves moderately convex and most 



prominent near the beak. Surface marked by concentric growth 

 lines. About yl^ inch in length. 



Maquoketa of Iowa and Wisconsin; Lorraine of Ontario. 



IX. Lingula Bruguiere. 

 Shell thin, glistening, generally smooth or with fine concentric 

 or rarely radiating striae ; generally equivalved ; broad anteriorly, 

 parallel sided or tapering posteriorly. Ordovicic-Recent. 



A. Rectangular (sides straight and nearly parallel); hinge extremities abruptly rounded 

 or truncate I. 



I. Surface nearly smooth and glossy , 22. L. elderi. 



I. Surface marked by concentric striae I. 



I. Striae strong, sharp. Shell large a. 



a. Radiating striae absent 24. L. iowaensis. 



a. Radiating striae present 20. L. rectilateralis. 



1. Striae fine b. 



b. Striae crossed by radiating lines 26. L. clintoni. 



b. Striae not crossed by radiating lines 29. L. cuyahoga. 



B. Oval or elliptical (sides curving) II. 



II. Small, not exceeding one-half inch in length 2. 



2. Length exceeding breadth c. 



c. Front subtruncate 32. L. subspatulata. 



c. Front broadly rounded f. 



f Beaks attenuate 23. L. modesta. 



f Beaks obtuse 27. L. ligea. 



c. Front regularly rounded ff. 



ff With flattening and faint radiating striae 30. L. melie. 



ff Convex, without flattening or radiating striae.. 31. L. umbonata. 



2. Length and breadth nearly equal 18. L. curta. 



II. Large, I inch long 17. L. cobourgensis. 



