NAIADES OF MISSOURI 59 



rtdae, medium in size, greatly inflated, characteristically sulcated 

 post-ventrad; dorsal ridge prominent, the slopes coarsely cos 

 tated; post-umbonal ridge prominent and profusely tubercled; 

 radial furrow deep and wide, in front of which another row of 

 rather scattered tubercles extend from the beaks post-ventrad 

 across the disk; epidermis dark yellowish. 



Internal Structures: — Identical with those of 0. quadrula. 



Sex Length Height Diameter Locality 



cf 63 X 59 X 35mm (Miss., R. Hannibal, Mo.) 



9 44 X 39 X 18 " ( " " " " ) 



cf 23 X 16 X 9 " (102 R., St. Joseph, Mo.) 



cf 15.5 X 6.5 X 7 " (Osage R., Schell City, Mo.) 



It may be that the juvenile shell measurement of the last 

 two above is only that of 0. quadrula since all juveniles of the 

 latter possess the characteristic sulcation at the post -ventral 

 portion of the shell as well as the profuse costation on the slopes 

 of the post-dorsal ridge; hence, the inferrence the author would 

 draw in asserting that 0. fragosa may be an occasional instance 

 of an overgrown shell of Q. quadrula. 



Miscellaneous Remarks: — This type of Conrad is of rare 

 occurrence in this State, the Mississippi being the only place 

 where anything like its type may be found with any degree of 

 assurance. Abnormal forms of fragosa are seen occasionally in 

 the headwaters of the Osage. vSimpson is not certain about the 

 distribution of fragosa outside of the Ohio and Tennessee — Cum- 

 berland systems. It is mainly distinguished from typical Q. quad- 

 rula by being more squarely quadrate, more inflated and the 

 upcurved tubercular costae on the rounded post-dorsal ridge 

 being more pronounced. It differs chiefly from aspera, (the small 

 Q. quadrula form of the Osage) in not being biangulated pos- 

 teriorly. It has been found to belong to the short period breeders. 



Quadrula aspera (Lea). 



("Little Rough Shell.") 



PL XVIII, Figs. 49 A and B. 



1831 — Unio asper Lea, Tr. Am. Phil. Soc, IV, p. 85, pi. IX, fig. 15. 



ANIMAL CHARACTERS. 



Nutritive Structures: — Branchial opening finely papil- 

 lose; anal smooth; supra-anal loosely, to deciduously, connected 

 to anal by mantle edges; inner gills much wider (posteriorly), 



