58 NAIADES OF MISSOirRI 



by rather coarse, irregular ridges, extending as tubercles on the 

 disk ; epidermis yellowish green with alternate bands of brown and 

 straw color. Interior of shell much like adult except not so broad, 

 nor as upright, nor as long; nacre white with light blue irridescent 

 sheen posteriorly. 



Miscellaneous Remarks: — Q. nodulata seems to be only a 

 globular-shaped Q. quadrula and is more typically a southern 

 shell; however, it is occasionally met with in the Upper Mississ- 

 ippi, where it is most found in this State. Mr. B. F. Bush col- 

 lected some miscellaneous shells from the interior of the state 

 and donated them to the United States Museum where some 

 were identified as this species. It is to be distinguished from Q. 

 pustulosa especially by two regular radiating rows of widely 

 separated tubercles obliquely arranged from the umbones to the 

 ventral margin on the posterior half of the disk; then, too, it is 

 more inflated, is not so upright, has greater umboidal ratio, has 

 more of an alated dorsal ridge and belongs to the so-called " Lach- 

 rymosa" Group, whereas, pustulosa is a member of the first group 

 of this Genus of which it is the type; hence, the latter is, after 

 all, not even closely allied. However, there is not much difference 

 between these two Quadrulae as to the form and size of their 

 larvae, and as to form of adult shell, it lies nearer to the variety, 

 contraryensis of Q. quadrula. Surber (1913, p. 113) finds this 

 species to be a gill parasite upon the crappie (Pomoxis annularis) 

 as an occasional host. As to its breeding habit, it is tachytictic. 



Quadrula fragosa (Conrad). 



("Hickory Nut Shell.") 



PL XVIII, Figs. 48 A and B. 



1836 — Unio fragosus Conrad, Monog. of Fresh-water Shells, II, p. 12, 

 PI. VI., fig. 2. 



ANIMAL CHARACTERS. 



Nutritive and Reproductive Structures: — Identical with 

 Q. quadrula as far as can be determined, with the scanty supply 

 of material at hand — none of which is in gravid condition. How- 

 ever, Wilson and Clark (191 4, pp. 59 and 60) report it with all 

 four gills marsupial, thick, pad-like. Glochidium unknown. 



shell characters. 

 ^;?cternal Structures: — Shell most quadrate of the Quad- 



