BRADLEY: BRACHIOPODA OF THE tfAQUOXETA OF IOWA. 523 



greatest convexity b little anterior <>(' the middle In the adult the 

 brachial-valve is marked by lamellose growth-lines that suggest 

 premature senility. Striations on the brachial-valve are fine, from 

 twelve t»> fifteen within 5 mm. <>n the anterior margin. They show 

 an unpronounced alternation <>l" two coarser encompassing one or two 

 finer striae. On the pedicle-valve they are finer, from seventeen to 



twenty in 5 mm. They show the same alternation as those of the 



brachial-shell. 

 A typical specimen measured: — 



Width Length Greatest convexity 



17 mm. 15 mm, 6 mm. 



Locality: — Lower Maquoketa at Clermont, Iowa. Holotype, 

 M. C. Z. 8,542. 



Strophomena sp. ind. 



A small specimen 16 mm. wide along the hinge-line, 12.5 mm. long, 

 and with a convexity of 3 mm., which equals the greatest height of the 

 cardinal area, shows a pathological dwarfed condition. Striae are 

 fine, five or six in 2 mm. and show T no alternation. Concentric lines 

 which tend to be prominent and lamellose are present. Concentric 

 striae are prominent near the posterior edge of the pedicle-valve and 

 form file-like indentations upon the radial striae. Retardation of 

 growth is noticeable on the brachial-valve where the first concentric 

 line is badly malformed. The pathological condition is so marked 

 that it is difficult to identify the species and justifies a separate 

 description. 



PORAMBONITIDAE. 



Parastrophia divergens Hall and Clarke. 



Parastrophia divergens Hall and Clarke, Pal. N. Y., 1895, 8, pt. 2, p. 222, 366, 

 pi. 63, fig. 4-7. 48th Rept. N. Y. state mus., 1897, 2, p. 364; pi. 10, fig. 

 11-14. 14th Rept. N. Y. state geol., 1897, p. 364, pi. 10, fig. 11-14. 



Shell of medium size; brachial-valve strongly, pedicle-valve weakly, 

 convex. The beak is erect; and the surface slopes gently to the 

 lateral margins. Half-way to the anterior margin the surface becomes 

 abruptly depressed, forming broad, deep, characteristic sinus, which 

 contains three well-defined plications. Two less-defined ribs occur 

 on each lateral slope. 



