328 THE PEARLY FRESH-WATER MUSSELS— SIMPSON. vol. xvm. 



lying north of about 40°; occupjang in all an area in the palearctic 

 region of something like 9,000,000 square miles. The Amoor River, 

 which takes its rise in Siberia and Mongolia south of the Stanovoi 

 range, has a mixed ISTaiad fauna whose characters partake of the 

 Pahearctic and Oriental provinces. Vnlo pictorum, a species common 

 to all Europe and Siberia, is found at Khabarovka, in the Amoor 

 Talley, as well as Anodonta magnijica, Lea, A. cellensis, Scliroeter, and 

 A. pJicata, Solander, which is synonymous with Crisfaria discoideus of 

 Lea, the latter three being common to Cbina.^ 



According to Middendorf,' Anodonta hercule((, Middendorf, a Japan- 

 ese species, which is a Cristaria; Unio monf/olicus, Middendorf (=t':«/o 

 marfiaritiferus, Linnfeus'O^ sbud Anodonta cellensis, Schroeter, are found 

 in the Amoor region. His Unio complaitatu.s, Solander, a common New 

 •England species, which he credits to Siberia, is, according to his figures, 

 without lateral teeth, and appears to be a stunted form of Unio mar- 

 garitiferus. 



Schrenck ' gives the following list of species of the Amoor Valley:* 



* TJnio mongolicus, Middendorf. 



* U. {Marg.) dahttricus, Middendorf. 



* Anodonta anatina, Linnn'us. 

 *A. cellensis, Schroeter. 



Unio grajifntus. Lea. 



*U. piciorum, Linnieus. 



*Unio (Marg.) margaritifcrus, Liinnxixs. 



Anodonta pJicata, Solander. 



A. magnifica, Lea. 



His U7iio grayamis is certainly not that species, but a shorter, heavier 

 shell, belonging, however, to an Oriental group; and the Ufiio mongo- 

 licm is most likely a form of Unio margaritiferus with imperfect laterals. 



The southern limit of the Pahearctic Region in North America can 

 not be accurately given, but it probably extends to near the Isthmus 

 of Tehuantepec, as one of the common Oaliforniau Anodontas has been 

 found in Oaxaca. 



In all this vast area there are perhaps not uiore than 50 valid species 

 of Naiades, which belong to the genera Unio, Leguminaia, Anodonta., 

 and the species of Cristaria alluded to, though the new school of 

 conchologists have considerably multiplied the genera and have run the 

 specific names up into the thousands. The species are, for the most 

 part, small to medium in size, without conspicuous sculpture or angles, 

 or, as a rule, any bright patterns of coloring. 



The group of Anodontas typified by the well-known A. cygnea, Liu- 

 nfeus, is distributed over this entire region, all the forms found in the 

 Pacific drainage of North America either belonging to it or being, 

 I think, closely related. One species, A. yukonensis, Lea, from the 

 Yukon River, Alaska, is absolutely identical with specimens of Ano- 



'On the authority of Moussou (Journ. de Conch., XXVII, p. 26). 

 ^Malacoz. Rossica, Sib. Keise, 1847-1851, p. 273. 

 sReiseu und Forsch. im Amur-Lande, 1854-1856, p. 694. 



■•Those belongine, properly to the palearctic region I have characterized by an * ; the 

 others are Oriental species. 



