SPIRIFERELLA 417 



9.4 mm., thickness 6.2 mm., length of hinge-line 5 mm., width of mesial 

 sinus in front 3.7 mm. 



Pedicle valve most convex posterior to the middle, the umbo prom- 

 inent, the surface curving abruptly to the cardinal margin, and more 

 gently to the lateral and anterior margins; the mesial sinus originating 

 at the beak, sharply defined throughout its entire length by a pair of 

 strong, rounded plications, rather shallow, of moderate width and round- 

 ed in the bottom, either without plications or with a single, simple median 

 one originating back of the middle of the shell and continuing to the 

 front margin with gradually increasing strength, but never becoming as 

 strong as those of the lateral slopes of the valve ; the beak prominent, 

 pointed, rather strongly incurved ; each lateral slope of the valve bearing 

 from four to six rounded, simple plications which originate along the 

 cardinal margin, the cardinal area small, concave, with the curvature 

 increasing towards the beak, the lateral margins not sharply defined, 

 the surface curving without interruption into the lateral slopes of the 

 valve. 



Brachial valve less convex than the pedicle, the greatest convexity near 

 the middle, the surface curving more abruptly to the cardinal margin 

 on each side of the beak, and gently to the antero-lateral margins, a 

 little compressed towards the cardinal extremities ; mesial fold well de- 

 fined from the beak to the front margin, scarcely elevated above the gen- 

 eral convexity in the posterior half of the valve, and only moderately 

 elevated towards the front, a little flattened on top or with a slight longi- 

 tudinal depression which is much fainter than the median plication in 

 the sinus of the opposite valve ; beak small, incurved, only slightly pro- 

 jecting beyond the cardinal margin; each lateral slope marked by from 

 four to six simple, rounded plications entirely similar to those of the 

 pedicle valve. Surface of both valves marked by very fine, closely 

 crowded granules or papillae, and the shell structure rather coarsely, but 

 closely, punctate. 



Remarks. In its general outline this little shell at once suggests a 

 minute individual of Spirifer suborbicularis or 8. chouteauensis, but it 

 differs notably from either of these species 'in the presence of the minute 

 surface papillae and the punctate shell structure. The punctate structure 

 of the shell suggests the genus Spiriferina, but the general form is totally 

 different from any of our other species of that genus, all of which have 

 a more or less elongate hinge-line and well defined cardinal area with 

 sharply defined lateral margins. The internal features of the shell have 

 not been observed so that the presence or absence of a median septum 

 in the pedicle valve is not known, if such a septum be present the species 

 should doubtless be placed in the genus Spiriferina, in spite of its unusual 

 external form. On the whole this little shell seems to agree most closely, 



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