NOTES ON THE UNIONID^E AND THEIR 

 CLASSIFICATION. 



V. STERKI. 



The Unionidae are not only the most conspicuous inverte- 

 brates of our fresh waters, and wonderfully rich in species, but 

 they are also very interesting morphologically and physiologically. 

 The publication of Simpson's synopsis of the Naiades, made a 

 new era in our knowledge of these animals. On the one hand, 

 Simpson has undertaken the important and difficult task of 

 revising the enormous number of described species by the care- 

 ful examination and comparison of an immense mass of material. 

 A large number of nominal species have been referred to those 

 which were believed to be valid, when reduced to synonyms and 

 varieties. On the other hand, he has shown that not only the 

 shells, but principally the soft parts, must be considered in order 

 to build up a proper classification and he has investigated and 

 sifted the attempts of earlier writers in that direction. 



Having studied for years such of our Unionidas, or, more 

 properly, Unionina\ as were obtainable, their soft parts, propa- 

 gation, and embryos, I have formed some ideas of my own regard- 

 ing their classification, which proves to be somewhat at variance 

 with that given by Simpson. At first it seemed preferable to 

 vat i 1 tudy and compare further, 1 until now, almost two 

 years later, I feel more satisfied than ever that these views have 

 a real foundation and some scientific value. 



