672 GEOLOGICAL SURVEY OF IOWA. 



Fig. 1. View of the anterior side of specimen, showing the truncated subradial plates. 

 Geological formation and locality. In the St. Louis limestone : St. Louis, 

 Missouri. 



Synbatliocriims swallovi ( n. s.). 



PLATE XVII. FIG. 8 & 9. 



BODY elongate : base small, somewhat truncate below, and 

 depressed for the reception of the column ; sutures of the 

 three divisions barely visible. First radial plates quadrangu- 

 lar, wider than long, except on the anal side, where two of 

 them are slightly truncated on their upper angles ; forming, 

 with the base, a shallow spreading basin. Second radial plates 

 quadrangular, wider than long, narrower above, subangular 

 in the middle of the upper half of the plate. Arms simple, 

 elongated, scarcely tapering : plates quadrangular, wider 

 than long, the lower ones obtusely angular in the middle, 

 those of the upper and middle part becoming regularly 

 convex. 



COLUMN composed of alternating longer and shorter plates, 

 with a shorter plate at every third, fourth or fifth articula- 

 tion : joints of the column deeply serrated on the articulating 

 faces. 



This species differs from the S. tcortheni of the Burlington limestone in being less 

 elongated, having a broader and shorter base, the depth of the calyx from the base 

 to the top of the first radials being not more than two-thirds as great as in the former 

 species; while the arm-joints are proportionally shorter. 



Fig. 8. A specimen somewhat distorted from pressure, with arm-joints less distinctly 

 angular than in the other specimen. 



Fig. 9. A specimen preserving a portion of the column, and having the summit broken 

 away f The plates of the arms are improperly represented in the figure as 

 opposite to each other, while they alternate; the two rays on the right hand 

 vary nearly a quarter of the length of the plate, and on the left ray the 

 sutures are opposite the centre of the plates of the adjacent ray.] 



Geological position and locality. In the St. Louis limestone, near St^ 

 Louis, Missouri. 



