86 Trans. Acad. Sci. of St. Louis. 



which are without doubt -good representatives of the species. 

 These specimens exhibit some variation in size and form. 

 The largest one measures 40 mm. from the beak to the 

 farthest posterior extension of the body of the shell, while the 

 same measurement in the smallest shell is scarcely 10 mm. 

 The specimens illustrated are intermediate in size. There is 

 also some variation in the width of the body of the shell, and 

 also in the posterior extension of the wing. In some individ- 

 uals the posterior angle of the wing reaches nearly as far as 

 the most posterior extension of the body of the shell, while in 

 others it is considerably shorter. 



This species has previously been referred to the genera 

 Avicula and P termed, but an examination of authentic speci- 

 mens shows that the species should be placed in the genus 

 Leiopteria. This species differs from the Devonian species of 

 the genus generally, in its greater obliquity and in its narrower 

 shell. L. speciosa M. and G. from the Chouteau limestone 

 near Sedalia, Missouri, closely resembles the Burlington 

 species and may be identical with it. 



Avicula strigosa (White). 



PI. III. f. 10. 



Pterinea strigosa. Bull. U. S. G. S. No. 153: 511. 



Shell very oblique, length, 30 mm., greatest height, 8 mm. 

 Hin^e-line slightly more than one-half the length of the shell. 

 Anterior and posterior extremities sharply rounded; ventral 

 margin convex; dorsal margin, exclusive of the wing, concave 

 with the concavity less than the convexity of the ventral mar- 

 gin. Beak placed near the anterior extremity of the shell. 

 Behind the beak there is a small, narrow, abruptly com- 

 pressed wing whose posterior extremity seems to be pointed. 

 Body of the shell very convex, the slope toward the dorsal 

 margin being much steeper than the ventral slope. The 

 o-reatest convexity at about one-third the length of the shell 

 from the anterior extremity. The anterior extremity forms a 

 small, inflated ear which is separated from the body of the 

 shell by an oblique depression. Surface marked by a few 

 concentric wrinkles which are more conspicuous anteriorly. 



Remarks. The form of the posterior wing of this species 



