THE NAIADES OF MISSOURI 141 



except A^. ellipsi formis when the former is young. However, the 

 more elliptic shell with broader, straighter rays would serve as 

 the main distinguishing features. vSurber (1913, p. 109) has found 

 that its glochidium is a gill parasite upon the white bass {R. 

 chrysops) as a natural host. Breeding records have been care- 

 fully kept for this species, especially for commercial reasons, to 

 find that it is typically bradytictic. 



Nephronaias ligamentina gibba (vSimpson). 



1900b — Lampsilis ligamenliuus gibbus Simpson, Proc. U. S. Nat. Mus 

 XXII.p. 540. 



("Southern Mucket," "Yello\Y Mucket.") 

 Animal Characters: — Identical with those of the parent 

 species, except, of course, in short gills and other modified parts 

 due to a shorter shell. The glochidia are the same. 



Shell Characters :— Shell "peculiarly short, humped form" 

 (Simpson) ; thicker, heavier more inflated with more roughened 

 growth lines and more of a yellowish epidermis than the parent 

 shell. 



Sex Length Height Diameter Locality 



cf 85 X 60 X 40mm (Osage R., Monegaw Springs) 



9 80 X 64 X 40mm ( " " Linn Creek) 



9 89 X 70 X 38mm ( " " Bagnell) 



Miscellaneous Remarks: — Gihha seems to be a rather 

 common variety throughout the southern range of the species 

 and is expecially characterized by the short, stout, "humped" 

 form of shell. Perhaps it bears the same relation to its species as 

 dakotana Frierson does to grandis Say. The writer's experience 

 in the study of the form of ligamentina while on a 300-mile float 

 down the Osage was that it was difficult to ascertain the point 

 of separation between the species and the variety, gihha, so imper- 

 ceptibly do they grade into each other. This form is met with in 

 drainage of the Ozark Center as well — especially in the Black 

 River. 



Nephronaias ellipsiformis (Conrad). 



("Ellipse.") 



PI. XXV, Figs. 86 A—D. 



1836 — Unto ellipsiformis Conrad, Monog. VIH, p. 60, pi. XXXI\', fig. I. 

 1845 — Unio spatulatus Lea, Proc. Am. Phil. Soc, IV, p. 164. 

 1898 — Lampsilis spatulatus Baker, Moll. Chicago, Pt. I, p. 106, pi 

 X, fig. 5; pi. Xin, fig. 2. 



