g22 Analysis of Periodical IVorks 



Valvata. a genus formed by Mliller, and of which the type 

 is Helix fascicidaris of Gmelin. The following is given as a 

 new species: 



Valvata dej)ressa. V. testa turbinata, imibilicata ; spira de- 

 pressa, obtusa ; apertura circinata, patula. 



Among the bivalves, M. PfeifFer has attempted a furthei- il- 

 lustration of the genera Anodonta {Anodo7i Sw.) and Unio. 

 Like all others who have preceded him, this author has drawn 

 the specific distmctions in this intricate group principally from 

 their size and contour. To those conchologists who have 

 formed extensive series of tliese shells, it will be almost un- 

 necessary to point out the fallacy of making species from such 

 characters ; because they are, above all others, the most vague 

 and inconstant ; so much so, that the shells from one pond sel- 

 dom agree perfectly in their form with those of another, and 

 thus species might be made ad injinitum. Mr. Swainson ap- 

 pears aware of this, and has directed our attention to the foi*m 

 of the lamellar plate to which the ligament is attached ; the 

 modifications of which, he conjectures, will pi-ove the best dis- 

 crimination of the species. This is a new view of the subject, 

 and certainly deserves investigation. Of the four species enu- 

 merated in this work, we consider the Anodonta cellensis only 

 as a variety (with a somewhat narrower sheU) of A. cyg7iea. 

 The Anodonta anatina may probably be a thick variety of 

 our British species ; and the Anodonta intermedia, we have 

 Mr. Swainson's authority for sayhig, is the same as his Ano-^ 

 don 2'>icttis, described in the Bligh collection. Lamarck's 

 Anodonta intermedia is conipomided of two species. This is 

 shown by his synonyms, one of which refers to Chemnitz 

 8. tab. 86. Jl 763, representing the young of A. anatinus ; and 

 the other to iheEncij. Meth. pi. 201. f. 2., which is Mr. Swain- 

 son!s A. pictus, and is a continental species. These erroneous 

 synonyms of Lamarck have likewise been repeated in this 

 work. 



Among the Uniones, some mistakes also occur: theLinnaean 

 Pictorum is given under the name of Unio rostrata, after 

 Lamarck ; while ovata is mistaken for Pictorum. On the other 

 ,hand, IJnio margaritifera is so well characterized, that we 

 shall give the specific definition ; and also that of another, de- 

 scribed as a new species, and which we think is really so, be- 

 ing intermediate between ovata, and the real batava, of the 

 continental but not of the English writers. 



Unio margaritifera. U. testa elliptica, crassa, nigricante ; 

 natibus subdepressis, decorticatis ; dente cardinali minuto, sub- 

 conico (obtuso, Ed.) laterali nullo. The true character of 

 this species is here for the first time defined ; it consists in the 



lateral 



