20 THE NAUTILUS. 



Ihering fails to find them oi] any of the South American Union- 

 idce he has examined, but he has probably overlooked the statement 

 of Lea^ that the glochidium of Unio firmus of Brazil is provided 

 with both of these appendages. 



Castalia was placed in the Mutelidcz by the Messrs Adams, 

 but Ihering shows that it is very closely and curiously related to 

 Unio. In the latter the short branchial siphon is open ; in the 

 former it is closed ; in Unio the lateral teeth are either smooth or 

 obliquely striated;'' in Castalia they are vertically ridged. He has 

 applied the name Castilina to a few species which stand between the 

 two genera, and has given it generic rank. But he shows that 

 there is a complete intergradation and connection from one end of 

 the chain to the other. In certain Castalias there is a typical ani- 

 mal, in others it is that of Unio, and in Castalina there is an almost 

 complete blending and crossing of characters. I have noticed on 

 examining large series of these shells that in some Castalias the 

 peculiar tooth sculpture is nearly wanting. 



Von Ihering finds that U7iio multistriatus of Brazil is very closely 

 related to N. senega/ ensis of Africa., and to certain Indian forms. 

 He has, in his collection, a specimen of Unio radula of India that is 

 identical with N. coriacetis from Rio Janeiro, and believes this fact 

 to be a proof of the long duration of the species of this family and 

 probably evidence in favor of the existence of the lost Atlantis. 



His arrangement of the families and genera stands as follows : 



Mutelidce v. Ih. (nee Adams). Unionidce v. Ih. (nee Ad.). 



Leila Gray. Hyria Lam. 



Glabaris (Gray) v. Ihering. Castalia Lam. 



Aplodon Spix. 



Plagiodon Lea. 



Fossula Lea. 



Mycetopus Orb. 



Solenaia Con. 



Mutela Scop. 



Iridina Lara. 



Pleiodon Con. 



Spatha Lea. 



Castalina v. Ih. 

 Unio Retz. 

 Margaritana Schum. 

 Cristaria Gld. 

 Anodonta Lam. 



^ Observations on the Genus Unio. 



^ In Onio torluostts Lea, a remarkable inequivalve species from China, the 

 laterals have perpendicular slrije, and Lea remarks that if this is found in all the 

 individuals of the species, it would have to be placed in Castalia. It has much 

 the appearance of Liiio ellipsis Lea. 



