STE. GENEVIEVE MARLS NEAR FORT DODGE 611 



centers of the clusters. Apertures regularly arranged, polygonal, 

 commonly hexagonal, varying in diameter from 0.28 mm. to 0.5 

 mm., in the clusters, nine or ten of the average size in three mm., 

 separated by comparatively thin partitions. Zooecial tubes curv- 

 ing gently throughout their length, not quite direct even at the 

 surface of the layers. Walls thin and flexuous below, but to- 

 wards the surface they become rather abruptly, but only moder- 

 ately thickened. Lines between walls of adjoining zooecia sharply 

 marked. Mesopores(?) (small tubes) very rare, only in the 

 groups of large zooecia. Diaphragms with large perforations, 

 three or four in each tube, quite commonly observed closing their 

 apertures. ' ' 



Occurrence. — Ste. Genevieve, Pella beds, Illinois Central rail- 

 road cutting, near Fort Dodge, Webster county, Iowa. 



BRACHIOPODS, 



OrtJiotetes Jiaskaskiensis (McChesney) 



Plate XII, figs. 21-22, 24. 



1914. Orthotetes l-askaskiensis Weller, Geol. SurA\ 111., ]\Ionog. I, 



p. 77, pi. VI, figs. 1-14, 15 ? 



Shell of medium to large size, subcircular in outline, broader 

 than long, hinge-line shorter than the greatest width. Cardinal 

 angles rounded. A nearly complete specimen at hand is of the 

 following dimensions : length of pedicle valve 26 mm., length of 

 brachial valve 24.5 mm., greatest width 38 ram., height of car- 

 dinal area 4.5 mm., thickness near midlength 5.7 mm. 



Pedicle valve flattened concave, greatest concavity near the 

 middle; beak and umbo abruptly elevated, and the whole umbonal 

 region somewhat distorted. Cardinal area flat and sloping back- 

 ward from the hingeline at a wide angle ; each half of the area 

 is divided into two regions by a line originating at its apex and 

 extending diagonally to the cardinal line and terminating at a 

 point midway between the center of the area and the cardinal 

 angle. Pedicle opening higher than wide and closed by a con- 

 vex deltidium. On the inside of the valve a strong median sep- 

 tum extends forward between the muscle scars. 



Brachial valve convex except near the cardinal extremities 

 where it is flat or slightly concave, highest convexity posterior to 

 the middle. Interior unknown. 



Surface of both valves marked by radiating cost® which in- 

 crease by the introduction of new ones betweea the old or by the 

 division of the older costge. Growth lines rather coarse, in some 



