SWALLOW — DESCRIPTION OF NEW FOSSILS. 91 



lias a small sinus. The caput-serpentis is more distinctly 

 cost ate than any of the allied species, or perhaps allied va- 

 rieties. 



The fossil is common in the Upper Coal Measures of Mis- 

 souri and Kansas. 



SpIRIGERA FORMOSA. 



Shell small, ovate, widest below the middle, usually gib- 

 bous, sinuate, punctate, trilobate. Ventral valve strongly 

 arched, gibbous near the beak ; beak large, strongly recurved, 

 truncate parallel with the border of the valves; foramen cir- 

 cular; mesial sinus deep and broad in front; (in depressed 

 varieties the front is prolonged into a Ungulate process 

 strongly curved up;) obsolete, or only a faint depressed line 

 towards the beak. Dorsal valve gibbous ; umbo full ; beak 

 recurved beneath the foramen, cutting its periphery ; mesial 

 fold high and rounded in front with a deep round sinus on 

 each side, rendering the shell subtrilobate. Surface punc- 

 tate ; marked with distinct lines of growth, with numerous 

 concentric striae, and with radiating striae when partially ex- 

 foliated. 



Measurement. A gibbous specimen — length, .49; width, 

 .44 ; thickness, .32. A depressed specimen — length, .48 ; 

 width, .41 ; thickness, .24. 



This little fossil was collected by Dr. Giddings in the upper 

 divisions of the Archimedes Limestone, above Boonville. 



Spirigera euzoxa. 



Shell small, ovate, sinuate and banded. Dorsal valve very 

 regularly convex, highest near the beak; sinus in front, with 

 a sharp depressed line in at the bottom; beak large, promi- 

 nent, incurved. Dorsal valve convex, highest above the mid- 

 dle, flattened towards the margins, with a sharp depressed 

 line from the middle to the front margin; itmbo full and 

 large; beak incurved beneath the foramen. Surface marked 

 with eight or nine broad, convex, concentric bands, with 

 three or four strioe between each pair. 



Length, .50; width, .46; thickness, .29. 



This beautiful fossil is rare in the middle Archimedes beds 

 in Cooner county. Collected by Dr. Giddings. 



Productus Americanos. 



Shell very large, ovate, very convex, strongly arched to- 

 wards the beak ; very much produced in front, costate and 

 striate. Ventral valve very convex in the middle; strongly 

 arched over the umbo to the beak; flattened or concave to- 

 wards the margins; elevated and rounded from the middle 



