SPIRIFEK 339 



Remarks. This species is a close ally of S. forbesi from the Burlington 

 limestone. In general form, proportions and size the two species are essen- 

 tially alike, but S. crawfordsvillensis is characterized by its coarser and 

 less numerous plications upon the lateral slopes of the shell, these being 

 only 12 or 14 in number, while in 8. forbesi they exceed 20. 



Horizon. Keokuk (Crawfordsville beds of Indiana). 



SPIRIFER WASHINGTONENSIS n. sp. 

 Plate XLIV, Figs. 1-14 



Description. Shell of medium size, much wider than long, the greatest 

 width along the hinge-line, the cardinal extremities angular. The dimen- 

 sions of a nearly complete individual are : length of pedicle valve 26.5 mm., 

 length of brachial valve 20.5 mm., width 41 mm., thickness 17.5 mm., 

 height of cardinal area 5.5 mm. 



Pedicle valve moderately convex, the convexity reaching to the car- 

 dinal extremities or with the surface compressed distally, the umbonal 

 region broad, the surface sloping abruptly to the cardinal margin and 

 more gently to the antero-lateral margin ; beak small, pointed, a little in- 

 curved; cardinal area of moderate height, nearly flat except just under 

 the beak where it is arched, the inferior flattened portion extends poste- 

 riorly nearly in the plane of the valve, the lateral margins are sharply 

 angular and slope with a gentle convex curve or in a straight line from 

 the beak to the cardinal extremities; lateral slopes of the valve each 

 bearing about 15 simple, rounded plications which grow successively 

 smaller towards the cardinal extremities, the last 2 or 3 sometimes becom- 

 ing very faint or obsolete : mesial sinus well denned at the beak, becom- 

 ing broader and less well denned anteriorly, it is shallow or of moderate 

 depth and is rounded in the bottom, a median plication originates near 

 the beak and continues without division to the anterior margin where it 

 is broad and strong, on each side is a single lateral plication which does 

 not attain the strength of the median one, originating from the inner mar- 

 gins of the bounding plications. 



Brachial valve subequally convex with the pedicle, the greatest con- 

 vexity near the middle, mesial fold originating at the beak where it is 

 bounded by furrows somewhat deeper than those between the plications, 

 scarcely or not at all elevated above the general surface in the umbonal 

 region, becoming moderately elevated in front, it is divided by a rather 

 deep median groove corresponding with the median plication of the oppo- 

 site valve, each lateral slope divided into two plications, all four of which 

 join in a single plication at the beak; lateral slopes convex towards the 

 middle of the valve, becoming somewhat compressed towards the cardinal 

 extremities, marked by plications which are similar in form and number 

 to those of the opposite valve. 



