200 Bryant Walker 



As Tellina cornea L. is the type of the genus Sphcerium, Conieola Cless. 

 is equivalent to Sphccriuru s. s. and is entirely superfluous. 



Subject to this amendment, his arrangement is the same as that proposed 

 by Dall (30, p. 7) in 1903. 



Genus PISIDIUM C. Pfeiffer, p. 189. 



Dall (1. c.) has proposed the following arrangement for Corncocyclas 

 (Pisidhim) . 



Genus CORNEOCYCLAS Ferussac, 1818. 



Subgenus Corncocyclas s. s. 



Section Corncocyclas s. s. Type : C. pnsUla Gmelin. 



Section Phymesoda Rafinesque. Type : Tellina virginica Gmelin. 



Section Pisidium C. Pfeiffer. T821. Type: Tellina amnica Miillcr. 



Section Cyclocalyx Dall, 1903. Type : Pisidium scholtzi Clessin. 



Subgenus Cymatocyclas Dall, 1903. Type: Pisidium comprcssum Prime. 



Subgenus Tropidocyclas Dall, 1903. Type: Pisidium hcnslounanum 



Sheppard. 



Only the typical species are mentioned and no attempt is made to dis- 

 tribute the North American species among the different groups. 



Sterki (1. c.) tentatively and without definition proposes the following 

 "groups" : — 



Pluminina Clessin, 1879. Type: P. amnicum (Miill). 



This is equivalent to Pisidium s. s. and therefore unnecessary. 



Lacustrina Sterki, 1916. Type: P. idahocnse Roper. 



Rivulina (Clessin, 1879) Sterki. Type: P. snpinum A. Schmidt. 



Fontinalina Sterki, 1916. Type: P. fontinalc Pfr. 



Fossarina Clessin, 1879 (restricted). Type: P. obtusale Pfr. 



PLEUROCERA, p. 151. 



Pl,EUROCERA KNOXENSE (Lea). 



According to Tryon (134, p. 427) this name will take the place of P. 

 modestum (I.ea), 1862, because lo modcsta Lea, 1861, is also a Pleuroccra. 

 This, of course, is conditional upon the latter proving to be a valid species. 



Pi.EUROCERA parkEri Tryon. 



This name has been proposed by Tryon (134, p. 427) for Trypanostoma 

 tortum Lea (Ibid, p. 84), 1862, on the ground that Mclania torta (Ibid, p. 

 117), 1845, has priority, being also a Pleuroccra. 



