174 Bryant Walker 



instances he had claimed that the reference of the prior species in such cases 

 to another genus "hberated" his own subsequent name. This under the 

 Code is quite erroneous. 



PlEurobEma utterbacki Frierson. 



Pleurobema utterbacki Frierson, Amer. Mid. Nat., IV, 191 5, p. 197, pi. \, 



figs. I2a-^b and pi. XX, figs. 63a-d. 

 Type locality : 'White River, Hollister, Mo. 



This species is a Fusconaia and a synonym of F. o::arkensis (Call) ac- 

 cording to Ortmann (84, p. 63). 



Genus LEXINGTONIA Ortmann, 1914. 



Lexingtonia Ortmann, Naut., XXVIII, 1914, p. 28. 



Type : Unio suh planus Conrad. 



"This genus stands near Pleurobema and BUiptio and differs from either 

 chiefly by the subcylindrical, red placentae, and by the beak sculpture." 



Genus UNIO Retzius, 1788. 



Unio complanatus (Dill). 



Unio pullatns inajuscitlus De Gregorio, Moll, di aq. dul. di Amer., 1914, p. 

 27, pi. 8, figs. a-d. 

 Haas has recently (50, p. 54) figured the original type of Spengler's 

 Unio violaceus, which appears to be an abnormal specimen of this species 

 and proposes to give precedence to Spengler's name. I have shown else- 

 where (162, p. 3) that this is not competent under the Code and that Dill- 

 Avin's name should be retained. 



Unio crassidens Lam. 



According to Ortmann (79, p. 266) this is the Unio nigra Raf. Vanatta 

 (140, p. 555) states that the shell so labelled in the Poulson collection is 

 this species. If identifiable from the original description, Rafinesque's name 

 would have priority. Utterback (135, p. 199) has quoted me as authority 

 for the statement that Quadrula trape.zoides (Lea) should be considered as 

 the Unio crassidejis of Lamarck. I have expressed that opinion in corre- 

 spondence and if the process of elimination could be strictly applied that 

 would be the result. But Dr. Pilsbry has suggested that the provisions of 

 the Code in regard to designating generic types apply equally well to the 

 cases of composite species, of which this is an example, and that, if this 

 rule does apply, Idea's statement (Obs., I, p. 199) of his examination of 

 Lamarck's types in 1832 amounted to such a designation and can not now 



