221 



Note on the Variation of the Spires in Seminula argentia 



(Shepard) Hall. 



J. W. Beede. 



[Abstract.] 



Owing to the systematic Importance and the rarity of good material of 

 the brachial frameworlv of the brachiopods. any light on the extent of in- 

 dividual variation of these parts is of considerable importance. In exam- 

 ining several specimens of Scitiiniila uryentia (sliepardi Hall, which show 

 the position and form of the spiralia, some remarkable results were ob- 

 tained. 



Both valves of this species are quite convex, old specimens always 

 being very ventricose. However, the species is very variable in form. 

 Four of the thirteen specimens were somewhat compressed, but it so hap- 

 pens that three of these approach the normal type very closely, while the 

 fourth does not vaiy from it greatly. Those showing greatest variation 

 have not been subject to any visible external deformation. 



The normal position of the spire is with the apex pointing to the side, 

 near the margins of the valves, at or a little in front of the middle of the 

 shell, which is also its widest part. In the central part of the cavity of 

 the shell the edges of the spire nearly or quite meet. Anteriorly they flare 

 apart leaving a subcirciUar opening. For convenience in this paper this 

 opening will be referred to as the frontal aperture of the spiralia. 



A specimen from the Topeka limestone, Upper Cual Measures, shows 

 the spires with the apex of one of them pointing almost directly forward 

 toward the anterior end of the shell, turned through an angle of about 90 

 degrees from its normal position; while, as nearly as can be determined 

 from the ground specimen, the apex of the other is directed toward the 

 median line of the pedicle valve just in front of the hinge. This specimen 

 was selected and ground nearly to the center because it was one of typical 

 form and perfect exteriorly. The remaining specimens are all from one 

 horizon in the PeiTuian of Cowley County, Kansas. One of these has the 

 spire turned through an angle of 45 degrees or more in a vertical direc- 

 tion (when held brachial valve up and hinge away from observer) point- 

 ing near the middle of the right side of the brachial valve, while the oppo- 

 site spire points toward the middle of the opposite side of the pedicle valve. 

 Another specimen from the same locality is intermediate between this and 



13— Academy of Science. 



