244 jMISSISSIPPIAN BRACHIOPODA 



without anterior or posterior prolongation, and without the thickening 

 along the symphysis of the lateral elements. 



Remarks. The only species of this genus recognized in our faunas 

 is so small that it has been impracticable to study its internal characters 

 by means of serial sections as has been done in the case of the larger 

 forms, but the centronellid character of the brachidium has been de- 

 tected in one specimen which is filled with translucent, crystalline 

 calcite. 



SELENELLA PEDICULUS (Rowley) 



Plate XXX, Figs. 34-39 



1901. Dielasma (?) pediculus Rowley, Am. Geol., vol. 27, p. 350, pi. 28, 



figs. 43-45. 

 1908. Dielasma ( f ) pediculus Rowley, Mo. Bureau Geol. and Mines, vol. 8, 



2nd ser., p. 80, pi. 17, figs. 57-59. 



Description. Shell minute, smooth, subovate in outline, longer than 

 wide, the greatest width near or posterior to the mid-length, the anterior 

 margin regularly rounded or slightty truncated in the middle, pointed 

 posteriorly. The dimensions of a large example are: length of pedicle 

 valve 4 mm., length of brachial valve 3.5 mm., greatest width 3.2 mm., 

 thickness 1.5 mm. 



Pedicle valve arched from beak to front with the curvature a little 

 more abrupt to the posterior extremity, also arched transversely with 

 the lateral slopes a little flattened, the greatest convexity of the valve 

 near the middle, the surface incurved towards the cardinal extremities 

 to form a small, pseudo-cardinal area ; mesial portion of the valve not 

 differentiated except sometimes a little flattened anteriorly; the beak 

 prominent, pointed, slightly incurved, projecting conspicuously beyond 

 that of the opposite valve ; delthyrium large, broadly triangular, par- 

 tially closed by a pair of deltidial plates which sometimes meet towards 

 the base of the delthyrium, but often failing to meet and so leaving 

 a triangular opening from the apex to the base, the foramen slightly 

 or not at all encroaching upon the beak of the valve. 



Brachial valve depressed convex, its depth about one-half that of the 

 pedicle valve, the surface curving more abruptly towards the cardinal 

 margin; mesial portion of the valve not distinctly differentiated, al- 

 though it is rather broadly flattened; the beak short, obtusely pointed, 

 incurved beneath the delthyrium of the opposite valve. Internally the 

 brachidium is centronelloid in form, without anterior or posterior pro- 

 longation, being essentially of the type characteristic of the genus 

 Selenella. 



Surface of both valves usually entirely smooth, when lines of growth 

 are present they are very faint and are restricted to the marginal 

 portion. 



