BRAOHIOPODA. 369 



Trematls ottawensis.] 



TREMATIS OTTAWENSIS Billings. 



FIG. 30. Billings' original figure of T. ottawensis. 



1861. Trematis ottawensis BILLINGS. Paleozoic Fossils, vol. i, p. 53, flg. 58. 



1892. - Trematis ottawensis HALL. Palaeontology of New York, vol. viii, pt. i, pi. ivG, flgs. 15-17. 



Original description: "Nearly circular; length a little greater than the width; 

 upper valve moderately and uniformly convex, most elevated about the middle; apex 

 small, obtusely pointed, slightly elevated, marginal. Surface with fine, radiating 

 striae, which increase by interstitial addition, sometimes closely crowded together, in 

 which case there are ten or twelve in the width of one line; occasionally more distant, 

 or from four to eight in one line. The intermediate grooves are divided into square 

 compartments by cross-ridges, which connect the radiating ridges, but are not con- 

 tinuous, those in one groove not corresponding in position with those in the adjacent 

 grooves, so as to form uninterrupted concentric lines. In specimens with the striae 

 closely crowded together only the radiating lines are distinctly visible, but the others 

 can always be detected in good specimens, on close examination. 



"Length from twelve to fifteen lines; width a little less than the length. Lower 

 valve unknown," 



Formation and locality. Rare in the Galena beds at St. Anthony hill, St. Paul. Also in the Trenton 

 limestone, Ottawa, Canada, and at Frankfort, Kentucky. 



Collector. E. O. Ulrich. 



Genus SCHIZOCRANIA, Hall and Whitfield. 



1875. Schizocrania, HALL and WHITFIELD. Palaeontology of Ohio, vol. ii, p. 73. 

 1892. Schizocrania, HALL. Palaaontology of New York, vol. viii, pt. i, p. 142. 



Description: "Shells subcircular in outline, inequivalve, unarticulated. Pedicle 

 valve flat or concave; apex subcentral. A deep triangular notch extends from just 

 behind the beak to the margin, where its arc is equal to about one-sixth of the 

 periphery. The apex of this broad pedicle-notch is occupied by a triangular trans- 

 verse plate varying in size with the age of the shell, but extending for one-fourth to 

 one-third the length of the opening. Surface marked by concentric-growth lines. 

 On the interior no muscular impressions are visible. Brachial valve more or less 



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