„,,, „ LA.MELLIBB,ANCHIATA. "573 



Whltella ventrioosa.l 



angular or sharply rounded and distinct quite to the postero-basal margin. An 

 obscure furrow in the middle of the flat cardinal slope. From W. ventricosa Hall, sp., 

 which seems to be its nearest congener, it differs principally in the greater sharpness 

 •and. prominence of the umbonal ridge. The anterior end is much too small and 

 ' short for W. rugatina, W. concentrica and . W. scofieldi. In each case other differences 

 might be mentioned, but those selected will, it is believed, suffice. 



Greatest length, 23 mm.; distance from beaks to posterior extremity, 22.5 mm.; 

 posterior hight, 16.5 mm.; thickness, 13 mm. Antero-ventral — postero-cardinal diam- 

 eter, 17 mm. 



Figure 23 is taken from a doubtful left valve, obtained from the lower Trenton 

 in Jo Daviess county, Illinois. As viewed now, this specimen represents an ancestral 

 form' or variety of the present species from which also W. ventricosa, W. truncata and 

 perhaps other species as well have been evolved. More and better material, however, 

 is necessary before such a view of its relations can be consdered either as proved or 

 disproved. 



Formation and locality. — ^The typical form Is from the middle Galena near Wykofl, Minnesota. 



Whitella ventricosa Hall, 



PLATE XLI, FIGS. 24—26. 



Edmondia ventricosa Hall, 1847. Pal. N. Y., vol. 1, p. 155. 



Not Palcearca ventricosa, Hall, 1859. Pal. N. Y., vol. ill, p. 271, and Twelfth Kep. State Cab., 



pp. 10, 68 and 95. {?=C^rtodonta huronensis BALLINGS.) 

 Not Cypricardites ventricosus Hall, 1862. Geol. Rep. Wis., vol. 1, p 438; nor Whitfield, 1882. 



Geol. Rep. Wis., vol. Iv, p. 209. {=Cyrtodonta, sp., undet.) 



Believing that this species is represented among the undetermined fragmentary 

 shells from Minnesota, I thought it well to give illustrations of authentic specimens 

 from the Trenton of New York. These were received in an exchange some time 

 ago. Quite recently I sent two of them to Prof. E. P. Whitfield, of the American 

 Museum of Natural History, who compared them with the original types of the 

 species and verified, the identification. 



An examination of the New York examples established what I had already 

 suspected from the original figures, namely, that the species is a true Whitella and 

 not, as is commonly believed, a Cypricardites or Cyrtodonta. Its place in the genus 

 will be seen at once, when compared with other species of the genus figured on 

 plates XL and xli. The shell was thin, the beaks were full and prominent, the 

 umbonal ridge, though not as sharply defined as in many other species of the genus, 

 is still a more conspicuous feature than in any species of Cyrtodonta, the hinge has a 

 narrow external ligamental area or escutcheon, and ridge-like supports for a posterior 

 internal ligament, but no posterior lateral teeth. In short, the species presents 



