SPIRIFER 325 



line -f-60 mm., thickness 23.5 mm., height of cardinal area 11.5 mm. The 

 dimensions of another specimen, less extended along the hinge-line are : 

 length of pedicle valve 24 mm., length of brachial valve 19 mm., width 

 along hinge-line 38.5 mm., thickness 20 mm., height of cardinal area 

 10 mm. 



Pedicle valve subpyramidal in form, the surface sloping from the um- 

 honal region to the antero-lateral and anterior margins with a very gently 

 convex curve, the slope becoming nearly straight beyond the middle of 

 the valve, curving somewhat more abruptly to the cardinal margin for a 

 short distance on either side of the beak, becoming slightly compressed 

 subparallel with the cardinal area towards the cardinal extremities; 

 mesial sinus well defined, originating at the beak where it is narrow and 

 shallow, becoming rapidly broader and attaining a moderate depth to- 

 wards the front, nearly flat across the bottom in front with gently sloping 

 sides; beak small, rather obtusely pointed, a little incurved; cardinal 

 area high, the inferior portion nearly flat and lying in an angle of about 

 90 degrees or a little less to the plane of the valve, the higher portion of 

 the area concave with the curvature increasing to the beak, the lateral 

 margins sharply defined and sloping in nearly straight or slightly convex 

 lines from the beak to the cardinal extremities. Surface of valve marked 

 by rounded, radiating plications, which occupy both the sinus and the 

 lateral slopes, the larger of which measure about 2 mm. from center to 

 center, from 12 to 17 are present upon each lateral slope, all of which are 

 simple and originate along the cardinal margin, growing successively 

 smaller towards the cardinal extremities, the plications of the sinus are 

 about six in number, the median one originates in the umbonal portion 

 of the valve and continues to the front margin without division, the lat- 

 eral ones all originate as offshoots from the inner sides of the lateral 

 bounding plications of the sinus and continue to the front without division 

 and essentially parallel with the median one. 



Brachial valve moderately convex with the curvature more abrupt to 

 the cardinal margin, becoming a little compressed towards the cardinal 

 extremities; mesial fold well defined, flat on top, sloping abruptly to its 

 lateral margins on the sides anteriorly, of only moderate height, becoming 

 rapidly broader towards the front; the beak small and obtuse, only 

 slightly protuberant beyond the cardinal margin, and slightly incurved. 

 Surface marked by plications entirely similar to those of the opposite 

 valve in form and number, all those of the fold originate through the bi- 

 furcation of the original simple plication at the beak and then through 

 the division of these two main branches from their inner margins, all the 

 plications continuing to the front in a nearly parallel direction. 



Surface of both valves, in addition to the plications, marked by very 

 regular, somewhat crowded, subimbricating, concentric markings, and by 

 occasional stronger lines of growth. 



