THE NAIADES OF MISSOURI 247 
any rate. The writer, too, has had the good fortune to find its 
glochidium for the first time and is figured here in this catalogue 
for the first (See Text fig. 5). Many were taken from Lost Creek 
of the Grand River drainage, May 3d, and also August 5th, most 
of which were gravid with glochidia on both occasions. Although 
winter observations have not as yet been made, still we would 
judge from these two records that this species is not tachytictic 
as in most Unioninae. However, like most of the members of this 
Sub-Family their conglutinates are ‘‘aborted’’ when removed 
from their natural bed. Simpson speaks of this species as being 
very susceptible to variation; however, the writer has not noticed 
any great variability in this State, where its distribution is rather 
wide, and has not seen any varieties worth listing except comptodon, 
which has also been reported for Central Missouri by Dr. Britts. 
Uniomerus tetralasmus comptodon (Say). 
(“Pond Horn Shell.’’) 
Not figured. 
1832— Unio comptodon Say, An. Conch., V, pl. XIII. 
1832— Unto geometricus Lea, Tr. Am. Phil. Soc., V, p. 28, pl. IV, fig. ro. 
ANIMAL CHARACTERS are the same as those of the species; 
so are also its shell characters except in its outline being more 
rhomboid, its epidermis being more of a dull drab—or uni-color 
in having more roughened growth lines and a more curved hinge 
line. 
Sex Length Height Diameter Locality 
2) (S00! xX. 40° 9X. 25mm (Grindstone Creek, Maysville) 
Mi7S Laxifor x: od.” (Lost Creek, Amity) 
POS) Kt SGN) X50)? i are 3 aaa 
MISCELLANEOUS REMARKS:—This variety is often found in 
the same bed with the species from which it is discriminated, as 
above indicated, by the character of its epidermis. On this super- 
ficial basis of epidermis color there are so many intergrades and 
for this reason it may be doubted whether this and other recorded 
varieties are really worthy of their names. Comptodon was col- 
lected by Dr. Britts in Clinton Co., and is now on exhibit in the 
Division of Mollusks of the U. S. National Museum under the 
number, 150402. According to Henderson (1907, p.87, pl. ii, 
figs. 7a and 7b) this variety predominates over the main species 
in Colorado. Dr. Scammon (1906, p. 337) reports it for Neosho 
County, Kansas. The writer has examined both sterile and gravid 
