40 Trans. Acad. Sci. of St. Louis. 



entirely from the cardinals, there being no connecting plate, 

 forming an angle of 130° with a line drawn through the tips 

 of the umbones to the tip of the anterior division of the car- 

 dinals ; anterior cicatrices distinct, very large, and very deeply 

 impressed, striate, sometimes roughened, deepest close to the 

 base of the cardinal teeth ; pallial cicatrix very deep anteriorly, 

 crenulate, and lightly impressed behind; posterior cicatrices 

 large, confluent, not at all impressed, concentrically striate, 

 the retractor pedis impression neither on nor very near the 

 end of the lamellar laterals ; dorsal cicatrices disposed vari- 

 ously, and always irregularly, in the cavity of the beaks, 

 sometimes quite central; nacre always rich purple, commonly 

 roughened with numerous small pear-like masses studding the 

 body cavity. 



Dimensions of large male: length, 165.00 mm. ; breadth, 

 66.00 mm. ; height, 116.50 mm. Dimensions of large female: 

 length, 141.50 mm. ; breadth, 68.15 mm. ; height, 96.76 mm. 



Unio pustulatus Lea. 



Trans. Am. Philos. Soc, Vol. IV, 1830, p. 79, PI. VII, 

 Fig. 9. Described from the Ohio. 



Unio nodulatm Ra6nesque. So Conrad, Monography 



of Unio, PI. XLV, Fig. 1, 1838; Reeve, in Conchologia 



Iconica, Vol. XVI, Unio Plate XIII, Fig. 51, 1864. 



This form is easily distinguished from the related species 



which follows, by the fewer pustules which are larger than in 



Unio pustulosus Lea, and are besides differently disposed over 



the disk. Moreover, its quadrate outline is dissimilar to that 



presented by any other of the pustulate Uniones. 



In the St. Francis river, at Wittsburg, the species occurs in 

 very great numbers, and is well developed and perfect ; it was 

 also found, sparingly, at Benton, in Saline river. It is so 

 well marked that very few synonyms have been made from 

 this shell, a fact that few other species will illustrate. 



Unio pustulosus Lea. 



Plates XIII-XV. 



Trans. Am. Philos. Soc, Vol. IV, 1830, p. 64, PI. VIII, 

 Fig. 7, from the Ohio and Alabama rivers; Reeve, in 



