112 THE NAUTILUS. 



to a casual collector. The swamps and " cray-fish land" offer 

 little attraction to ambitious snails, and even the hill country 

 has not yet organized a moUuscan colonization bureau. In the 

 cretaceous limestones of the central area the conditions are a 

 little more promising. The entire portion of the County lying 

 east of the Ouachita river is typical tertiary soil, but there are 

 no exposures of strata in these lowlands, and fossils are to be 

 secured only from occasional well borings. 



Since there are many creeks and bayous the collector would 

 expect a few colonies of Sphaeriidae, or at least a larger list of the 

 Lymnaeidse. As will be seen, however, the Unios fully makeup 

 for any disappointment on this score. Not only are there many 

 species and varieties, but specimens in finer condition could not 

 be desired. The mussel beds of the Ouachita river, while 

 worked to some extent for pearls, have not been found profit- 

 able, and button factories are too far away to make the expor- 

 tation of shells for commercial purposes practicable. From the 

 mouth of the Caddo river (five miles above Arkadelphia), the 

 Ouachita abounds in mussel " beds " throughout the rest of its 

 course, and the accessible and prolific breeding "bars" are less 

 disturbed than is usually found in the experience of the uniol- 

 ogist. Arkadelphia was at one time the head of navigation, but 

 steamers now seldom ascend the river above Camden. 



"Old River," the type locality of the genus Arkanma, is 

 really an "ox-bow" lake, a former channel of the Ouachita, 

 and it is still connected with it by a small creek w'hich does not 

 appear to dry up in summer. Its mouth is about two miles 

 north of Arkadelphia on the left bank, almost lost in a rather 

 dense and difficultly passable swamp. Here, and for a mile or 

 more up stream, Old River is deep and rather wide, with a very 

 sluggish current. In this habitat are found very large speci- 

 mens of Anodonta suborbiculata Say, which are of great beauty, 

 and the largest specimens of Arkatisia wheeled Walker and Ort- 

 mann. One of the latter measured 109.25 by 87 by 58 mm. 

 In the summer "Half-Moon Lake," the upper channel of Old 

 River, is set off by the subsidence of water on the sand bars, 

 and through the narrow creek which connects it with its lower 

 course it is quite impossible to navigate even a small canoe. 



