INVERTEBRATES. 133 



compressed, extending beyond the cardinal border, and located 

 about one-fourth the entire length of the shell behind the an- 

 terior extremity. Surface of the cast ornamented with rather 

 strong parallel lines of growth. 



Length 3 9 / 16 inches; height from the beak to the basal mar- 

 gin 1% inches: convexity of the valves about T /i 6 inch. 



This species resemblns .1. subcuneata in size and form, but 

 larks the concentric undulations of that species. 



Position and locality: Keokuk limestone, Warsaw, 111. 



Collector, A. H. Wort hen. 



Xo. 2540 of the Illinois State Museum. 



ALLOT? SMA ELOXUATA. Wort-hen. 



PI. XIX, Fig. 10. 



Allorisma elongata, Worthen. March, 1884. Bulletin No. 2 of the Illinois State Museum 

 of Natural History, page 12. 



Shell large, very elongate, dorsal and ventral margins nearly 

 straight and parallel: length three times as great as the height; 

 greatest convexity in the umbonal region: cuneate and perhaps 

 a little gaping behind, with a rather narrowly rounded outline. 

 Beaks recurved, approximate, and located near the anterior ex- 

 tremity. Anterior margin evenly rounded. The surface of the 

 cast shows numerous concentric undulations that are much 

 smaller and more numerous than in .4. subcuneata. its nearest 

 representative form. 



Length 3 15 / 16 inches: height 1 5 / 16 inches; breadth near the 

 umbo 1% inches. 



Position and locality: Keokuk limestone, Warsaw, 111. 



Collector. A. H. Worthen. 



Xo. 254:2 of the Illinois State Museum. 



