PALEONTOLOGY OF IOWA. 715 



UMELLIBRANCHIATA OF THE COAL MEASURES. 



GENUS ASTARTELLA ( n. g.). 



SHELL bivalve, thick, smooth or concentrically furrowed : 

 lunule impressed; ligament external; hinge-teeth two in 

 each valve, the anterior tooth of the right valve large and 

 strong, with a longitudinal pit in the summit. Related to 



ASTARTE. 



The hinge and teeth of but a single species have been observed, but the characters 

 seem to be sufficiently distinct to constitute a separate genus. 



Astartella vera(n. s.). 



PLATE XXIX. FIG. 1 a, b, c. 



SHELL somewhat rhomboid-ovate, gibbous on the umbones : 

 beaks subanterior, elevated, approximate ; anterior end 

 slightly concave below the beak and rounded below, poste- 

 rior end obliquely subtruncate. An oblique undefined ridge 

 extends from the beak to the posterior basal margin, having 

 the space between it and the ligamental area flattened : 

 lunule cordiform, strongly impressed ; ligamental area deeply 

 marked, and extending to the posterior extremity. Anterior 

 and posterior muscular impressions distinct; hinge strong. 

 Teeth of right valve separated by a deep pit ; the anterior 

 tooth with a longitudinal pit in the summit, and a callosity 

 on the inner margin at its base. 



SURFACE marked by strong concentric furrows, which are 

 separated by sharp angular ridges ; the intermediate spaces 

 finely striated. 



Fig. 1 a. View of the exterior of the right valve. 

 Fig. 1 b. Interior of the same, showing the teeth, etc. 



Fig. 1 c. Cardinal view of another specimen, showing the impressed lunule and 

 ligamental area. 



Geological formation and localities. Coal measures : Illinois and Indiana, 



