70 NAIADES OF MISSOURI 



southern drainage of the Missouri River. Simpson reports it for 

 the Mississippi drainage generally. A three hundred mile survey 

 of the Osage River, beginning at the headwaters, reveals the shell 

 of this species in all its external form and nacre-color extending to 

 granifera and even including Pleth. cooperianus. Variation in nacre- 

 color for this species is remarkable; however, this deviation from the 

 unipurple nacre of the type may be due to local reaction since it is 

 most noticed in the Osage below the region of medicinal springs. 

 Its favorable habitat is that of rocky shoals, but is occasionally 

 found in deep, quiet water with mud bottom where it acquires a 

 smoother, heavier and less inflated shell. The writer has had the 

 good fortune to secure, for the first time, several individuals gravid 

 with mature glochidia. The larva is found to be somewhat smaller 

 than that of R. granifera and with hinge line shorter and straighter; 

 as to form, and even as to size, it is hardly distinguishable from 

 granifera when allowance is made for variation in a large series. 

 This glochidium is figured and described here Jor the first time (See 

 Plate I, Fig. 4). It is observed by the writer to be gravid from June 

 \ until the middle of August, bearing ripe glochidia mostly about 



the middle of July. It is decidedly a short period breeder. 



Z""'^-^" Rotundaria granifera (Lea). 



("Purple Warty Back," "Purple Pit.") 

 PL XIX, Figs. 55 A and B. 

 1838 — Unio graniferus Lea, Tr. Am. Phil. Soc, Vi, p. 69, PI. XIX, fig. 60. 

 1900b — Quadrula granifera (Lea) Simpson, Proc. U. S. Nat. Mus., 

 XXn, p. 795- 



ANIMAL CHARACTERS. 



Nutritive Structures: — Identical with those of R. tuber- 

 culata in all respects. 



Reproductive Structures: — Typical specimens from the 

 Mississippi show the outer gills marsupial; conglutinates same 

 color and form as those of R. tuberculata; glochidium measures 

 0.290 X 0.350mm., being a little larger with more of an undulated 

 hinge line, but with the same general form. 



SHELL characters 



External Structures: — Like R. tuberculata except smaller 

 rotund, upright, alated, inflated, — especially fuller, higher, more 

 antero-protruding beaks and with more of a rayed character of 

 epidermis on anterior umbonal slope. Interior of shell identical 



