NAIADES OF MISSOURI 39 



Cragin while Mr. Frierson would assign it to undulata variety Pilshry 

 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 Amh. plicata costata (Raf.) and is far from 

 either Amb. rariplicata (Des.) or peruviana (Lam). vSince there are 

 few intergrades above or below quintardi 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.") 



PL XVI, Figs. 39 A—D. 



1820 — Amblema costata Rafinesque, Monograph of Biv. Moll, of R. 



Ohio. 

 1823 — Unio iindulatus Barnes, Am. Jour. Sci. and Arts, ist. ser., VI, 



p. 120, fig. 2. 

 1900b — Quadrula undulata vSimpson, 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 



