200 Bryant Walker 



As Tellina cornea h. is the type of the genus Sphcerium, Corneola Cless. 

 is equivalent to Sphcrrinm 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 Corncocydas 

 (Pisidium) . 



Genus CORNEOCYCLAS Ferussac, 1818. 



Subgenus Corneocyclas s. s. 



Section Corneocyclas s. s. Type : C. pusilla Gmelin. 



Section Phymesoda Rafinesque. Type : Tellina virginica Gmelin. 



Section Pisidium C. Pfeiffer, 1821. Type: Tellina amnica Mijller. 



Section Cy do calyx Dall, 1903. Type: Pisidium scholtsi Clessin. 



Subgenus Cymatocydas Dall, 1903. Type: Pisidium compressum Prime. 



Subgenus Tropidocydas Dall, 1903. Type : Pisidium henslozmanum 



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. 



Laciistrina Sterki, 1916. Type : P. idahoense Roper. 



Rivnlina (Clessin, 1879) Sterki. Type: P. supinum A. Schmidt. 



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



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



PLEUROCERA, p. 151. 



Pi,EUROcERA knoxense; (Lea). 



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

 modestum (Lea), 1862, because lo modesta Lea, 1861, is also a Pleurocera. 

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



Pleurocera parkeri Tryon. 



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

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

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



