NAIADES OF MISSOURI 121 
Cragin while Mr. Frierson would assign it to undulata variety Pilsbry 
Marsh; however, comparisons of these two forms seem to indicate 
that they are so identical as to assign the latter, through rules of 
priority, to the synonomy of the former. Dr. Ortmann, who has 
examined the anatomy as well as the shell characters of this con- 
fusing form, considers it as more like Amblema costata (Raf.) and 
suggests the reason why the writer should only find this little 
“Blue Point”? gravid during a six week’s survey of the Osage 
River was that the larger Amblemae were probably males of the 
same species although such sex dimorphism has not been observed 
in this genus before. Prof. Clark would also assign this form more 
to the undulata (Barnes) than to the plicata (Say) group. It has 
also been considered as very near undulata variety latecostata (Lea). 
Dr. Surber would not refer it to either group. One thing is certain, 
that it is not the typical Amb. plicata costata (Raf.) and is far from 
either Aimb. rartplicata (Des.) or peruviana (Lam). Since there are 
few intergrades above or below quintard: and since it is 
also such an abundant shell for this state and Kansas it is hoped 
that its assignment here settles it fairly well in this genus. The 
identical form is common in the White, St. Francis, Black and other 
southern streams of the Ozarks as well as in the drainage basins 
of the Osage, Gasconade, Meramec and other streams of the north 
slope of the Ozark Uplift. However, this sub-species is not found 
in North Missouri. Hence its habitat is more that of the swift, 
clear-water streams. Its breeding season is found to be the same 
as that of its parent species. 
Amblema (plicata) costata (Rafinesque) 
(‘“‘Wash-Board,”’ “‘Three-Ridge,”’ ‘‘ Blue-Point.’’) 
‘‘Flat-Plicate,’’ ‘‘ Fluter.’’) 
PIV i igs. 30° A=, 
1820—Amblema costata Rafinesque, Monograph. of Biv. Moll. of R. 
Ohio. 
1823— Unio undulatus Barnes, Am. Jour. Sci. and Arts, 1st. ser., VI, 
DE eOttory ae 
1900b—Quadrula undulata Simpson, Proc. U. S. Nat. Mus., XXII, 
p. 769. ; 
1912b—Crendonta undulata Ortmann, An. Car. Mus., VIII, pp. 246-247. 
ANIMAL CHARACTERS 
Nutritive structures, as well as the reproductive, are identical. 
with those of Amb. rariplicata in every respect. Even the glochidia 
