NAIADES OF MISSOURI 145 
INTERNAL STRUCTURES:—Cardinals heavy, ragged, double in 
left usually single in right; laterals long, rather straight and 
heavy; beak cavities deep; nacre marble white, occasionly pink, 
irridescent posteriorly 
Sex Length Width Diameter Locality 
OO MLGOKe Xa Soi, Xe AS (Grand R., Darlington) 
Cin Om sexe 80 eX Aa! (Platte R., Agency Ford) 
COMO Me axanys Ouuexanes © (Osage R., Warsaw) 
SX s Ole Xone s (White R., Hollister) 
No juveniles obtained. The last measurement is that of the 
youngest verrucosa obtanied. Its beak sculpture and disk are 
entirely sculptured with nodules and tubercules. The slope of 
the post-dorsal ridge are sculptured with three or four coarse, 
costated: undulations and with numerous fine costae arranged 
dorsad; shell very greatly compressed; nacre bluish. 
MISCELLANEOUS REMARKS:—40. verrucosa is the most peculiar 
species of its genus on account of the sexual dimorphism of its shell. 
For this reason especially, Simpson created a special genus (7rito- 
gonia) for it. Some students are inclined to think that 7ritogonia 
deserves sub-generic rank at any rate, because of its morphological 
departure form the typical Quadrula shell. Its soft parts, however, 
are so identical with those of the typical Quadrula that there is no 
- reason for its groupings with any other genus. Even though the 
form of the shell may be differnt, yet its conchological parts corre- 
late with those of other Quadrulae. Although Rafinesque’s figure 
of this species is abomnable, yet an unbiased study of it, together 
with that of his good description, would give preference for the 
adoption of his verrucosa over that of Barnes’ tuberculata. Like 
Q. quadrula, its breeding season is about as eccentric, in that the 
mature glochidia are not retained in the marsupia for any length 
of time; hence this accounts for the great difficulty of securing its 
larvae for study. Surber was fortunate in securing specimens 
with ripe glochidia June 1oth. The writer would judge from this 
record and that of his own (1. e., sterility for the Fall and Winter 
months) that this species is tachytictic. Vercucosa has the widest 
distribution for this State: however, it varies somewhat in size, 
inflation, disk sculpture, nacre-color for the different sections of 
the State; e. g., the pink-nacred ones are exclusively confined to 
the Southern Missouri streams, 
