THE NAIADES OF MISSOURI ' 145 



that the soft parts are those of Nephronaias. The shell was 

 identified later as ozarkensis of Call. 



SHELL CHARACTERS. 



External Structures: — Shell sub-elliptical, smooth, rather 

 compressed; post-umbonal slope somewhat biangulate by siphonal 

 ridges; beaks not prominent, sculptured by three fine undulations; 

 epidermis brownish-yellow or olive with numerous fine green 

 rays over central portion of disk; sexually dimophic. 



Internal Structures: — Cardinals tend to double in both 

 valves, laterals rather short, slightly curved; nacre usuaPy white, 

 sometimes salmon or pink, irridescent; muscle scars confluent. 



Sex Length Height Diameter Locality 



9 550 X 35.0 X 21.0 (Jack's Fork, Current R.) 



<^ 54-5 X 32.7 X 15.2 (Jack's Fork, Current R.) 



Miscellaneous Remarks: — The latter measurement is that 

 of Call's taken for a shell from the same locality (which is one of 

 the type localities of ozarkensis) as for the shell of the first measure- 

 ment which is now in the hands of th*^ writer through the kindness 

 of Mr. B. F. Bush, but which is now too much damaged through 

 shipment for figuring. Its shell is very much like that of N. pleasit 

 as to general outline, but is a little thicker and has a diflferent 

 nacre and epidermis. Forms of this Species reported by Meek 

 and Clark (1912, p. 18) for the White River drainage and described 

 as like "a very elongated Quadrula coccinea" and also identified 

 by Mr. Walker as " Pleurobemae rather than species of Lamp- 

 silis" are doubtless only Pleurohemae utterbackii of Frierson. 

 Definite assignment to the latter may be made for shells received 

 from the White River, Hollister, Missouri, under the name of 

 ozarkensis with the note: — "although not having Lampsiline 

 beak sculpture." The reader is invited to compare descriptions 

 and illustrations of Neph. ozarkensis and Pleu. utterbackii and note 

 that the shell of the former does not possess such tumid beaks, 

 nor such a furrowed post-slope, nor such distinct muscle scars, 

 and its shell has its whole facies of a thinner, lighter character, 

 thus being more inclined to a Lampsiline structure. 



Genus Amygdalonaias Crosse and Fischer. 



1893 — Amygdalonaias Crosse and Fischer, Jour de Conch., pp. 31-32; 

 1900b, — Simpson, Proc. U. S. Nat. Mus., XXII, p. 604 (as subgenus for 

 Plagiola). 



