96 THE NAIADES OF MISSOURI 



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 vState, 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, pi. XIII. 

 1832 — Unio geometriciis Lea, Tr. Am. Phil. Soc, V, p. 28, pi. IV, fig. 10. 



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 



9 80 X 40 X 25mm (Grindstone Creek, Maysville) 



9 75 X 40 X 24 " (Lost Creek, Amity) 



? 63 X 33 X 20 " ( " " " ) 



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 m the 

 Division of Mollusks of the U. vS. National Museum under the 

 number, 150402. According to Henderson (1907, p. 87, pi. 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 



