77/r ruiiiui of the Ma.vi'illr Limestone. 



371 



the beak and gradiiall}- increases in size to near the margin where 

 it rapidly expands into a trumpet-sha|)ed opening. Hinge line 

 straight, of medium length, with medium sized auricular extrem- 

 ities. Surface marked l)y tine radiating plications, which in- 

 crease in number by Iji furcation or insertion, and many of which 

 decrease in num1:er 1)\- coalescence at a j^oint just posterior to 

 the ex])ansi()n of the anterior margin. Auricular margins. 



a c 



Fig. 8. — Productus pileifoniiis. 



a. — A view of a pedicle valve, the anterior margin of which is 



more or less broken. 



b. — A view of the internal portion of the umbonal half of a brachial 



valve and the external portion of the anterior half of the 

 pedicle valve. 



c. — Profile view of a specimen (with a broken beak) showing the 



trumpet-like expansion of the anterior margin of the shell. 



marked by prominent concentric wrinkles which disapjjear at 

 the side of the shell so that the umbonal region is free from 

 them or so that the latter region is marked l)v onlv faint repre- 

 sentations of tliem. 



brachial valve sliglitlv concave in the umbonal region, sud- 

 denly reflected at the anterior margin to conform to the pedicle 

 valve, into whicli it is dee])l\- witlidrawn. Interior (?) siu-face 



