274 NEW YORK STATE MUSEUM 



region, hinge line straight and not extended, commissural margin 

 subcircular. Surface radii numerous, composed of rounded lines 

 with very narrow interspaces, the former increasing quite irregu- 

 larly by bifurcation but keeping a subequal appearance throughout. 

 The surface seems to have been early subject to irregular growth 



Leptostrophia tardifi 



from injury or pathologic condition of the mantle, rapid duplica- 

 tion of the striae following each of these cicatrices. These striae 

 are covered by extremely fine concentric lines. Attention is 

 directed to the differing expressions of the surface markings on 

 these allied species, L. t u 1 1 i a Billings, L. magnifica Hall, 

 L. i r e n e Billings and L. tardifi. 



Dimensions. Average specimen 35 mm in width on the hinge, 

 length 25 mm. 



Lower Devonic. Perce rock, P. Q. 



Leptostrophia magnifica Hall protype parva nov. 



This shell may be best expressed in terms of the widespread 

 L. perplana Conrad and L. b 1 a i n v i 1 1 i i Billings, for it 

 approaches these in all general features. Analysis of its structural 

 details however shows : 



1 The surface striae, fine, threadlike and crowded, exhibit some 

 diversity of size in early growth and this becomes intensified later 

 so that about the margins there is either an inclination to irregular 

 swelling or to fasciculation, the latter at times being quite pro- 



