UNIONIDAE WITH ABNORMAL TEETH 289 
‘THREE PSEUDOCARDINALS IN RIGHT VALVE: 
Lampsilis ventricosa, @, 6 yrs., (1 lateral in left valve); ¢ 
= 10-12 yrs. 
Lampstlis luteola #, 6 yrs. 
A study of the frequency of occurrence of diseased and abnor- 
mal freshwater mussels seems to indicate: 
; That certain weak-toothed genera, like Symphynota and 
; Alasmodonta have very rarely abnormalities of any kind. 
That, in the order of frequency of occurrence, the Anodontoid 
genera and Lampsilis ventricosa and Lampsilis luteola, are com- 
_ monly affected by trematode parasites, which disfigure the shells 
: internally. 3 
| That the presence of garbage, especially sewage, in the water 
apparently conduces to the well-being of these parasites, while 
anodontoid shells from clear ponds are in very many cases entirely 
_ free, as a community, from these parasites. 
In certain of the most common and widely distributed genera 
and species, especially L. luteola and L. ventricosa, the teeth are 
often defective through what has been called ‘“‘dental caries,’’ in 
_ which the horny material of the ligament and periostracum has 
_ replaced the shelly substance of the hingearea. 
Quadrula, Pleurobema, and similar genera with heavy shell 
and teeth, are, as a rule, generally normal. 
AN ANNOTATED PARTIAL BIBLIOGRAPHY, ARRANGED CHRONO- 
: LOGICALLY, OF PAPERS ON THE SUBJECT. 
. Lea, Isaac. Description of a New Genus of Naiades. ‘Tr. 
meAm. Phil. Soc., 1829, [J/I: 403-457, 8 plates. [1830]. At page 
428, pl. viii, fig. 11, is described Unio heterodon (=Alasmodonta 
heterodon (lea) Simpson,) from the Schuylkill. The species is 
_ very variable, as the laterals in each valve may be single, double 
or triple. 
H ConraD, Timotuy A. Descriptions of New Fresh-Water and 
Marine Shells. Ji. Acad. Nat. Sci. Phila., 1850, pp. 275-278, 2 
» plates. At p. 276, pl. xxxvii, fig. 7, may be found description of 
‘Unio contrarjus (=Lampsilis contraria (Conr.) Simpson). ‘The 
Iceality, (Ogeechee River, Georgia,) Simpson considers doubtful, 
and opines that this species may be simply a small male specimen 
_ with reversed laterals. 
4 AGassiz, Louts [Communication on Abnormal Shells| Proc. 
