BRADLEY: BRACHIOPODA OF THE MAQUOKETA OF loWA. 515 



Left u bm \ b n \i<>\ di, sp. now 



Plate 2, fig, 3, 4. 



Shell small; hinge width L5 to 17 nun., which is the greatest width 

 of the shell. Length, 9 to LO mm. Pedicle-valve convex and strongly 

 deflected near the anterior margin. The concave brachial-valve 



follows closely the convexity of the other. Cardinal area on the 

 pedicle-shell narrow, never exceeding 2 mm. in width, with a small 



triangular deltidimn. No interior known. 



The surface of some specimens is marked by fine radiating striae 

 which grow heavier on the deflected area of the pedicle-valve. In 

 most cases these striations are not noticeable and never attain the 

 prominence of those on L. unicostata, which is common in the Upper 

 Maquoketa. A strong mesial line is present on the pedicle-valve 

 and often bifurcates before it reaches the anterior margin, in some 

 specimens very near the hinge line. 



Local it j/: — Lower Maquoketa at Clermont, Iowa. Holotype, 

 M. C. Z. 8,545. 



Several species of Rafinesquina and Strophomena occur plentifully 

 in the Upper Maquoketa at localities north and west of Clermont, 

 Iowa. R. hingi (Whitfield), S. cardinalis (Whitfield), and S. fluctuosa 

 oecidaiialis Foerste, common in the Maquoketa of other Upper 

 Mississippi Valley localities, w r ere not found by the writer. 



A general characteristic of the new species of Rafinesquina and 

 Strophomena described below is that they are considerably smaller 

 than species from other localities in the Richmond. This dwarfing 

 may have been the first manifestation of the force wdiich drove both 

 genera to extinction at the close of the Ordovician. 



Although dwarf faunas were common in Palaeozoic times, as they 

 are now, it is not always easy to determine the cause. In the case of 

 the one under discussion, there were probably many contributory 

 causes. It appears that any change from the usual environmental 

 conditions affect the sensitive soft parts of marine invertebrates. 

 Professor Shinier says on this point, " Whatever ill or good conditions 

 the animal is subjected to are expressed in the shell, as moist and dry 

 summers are recorded by the annual rings of exogenous trees." 



With the universal uplift that came as the grand finale to the 

 Ordovician period, many changes were wrought that had great in- 

 fluence upon life in the sea. With the receding of the waters, lakes, 

 and shallow bays were formed that lost their connection with the 



