20 THE NAUTILUS. 
Ihering fails to find them on any of the South American Union- 
ide 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 Mutelide 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 Custilina 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 Unio multistriatus of Brazil is very closely 
related to N. senegalensis of Africa, and to certain Indian forms. 
He has, in his collection, a specimen of Unio radula of India that is 
identical with NV. coriaceus 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: 
Mutelide v. Ih. (mee Adams). Unionide y. Ih. (nec Ad.). 
Leila Gray. Hyria Lam. 
Glabaris (Gray) vy. Ihering. Castalia Lam. 
A plodon Spix. Castalina v. Th. 
Plagiodon Lea. Unio Retz. 
Fossula Lea. Margaritana Schum. 
Mycetopus Orb. Cristaria Gld. 
Solenaia Con. Anodonta Lam. 
Mutela Scop. 
Tridina Lam. 
Pleiodon Con. 
Spatha Lea. 
1 Observations on the Genus Unio. 
*In Unio tortuosus Lea, a remarkable inequivalve species from China, the 
laterals have perpendicular striz, and Lea remarks that if this is found in all the 
individuals of the species, it would have to be placed in Cas¢a/ia. It has much 
the appearance of Unio ellipsis Lea. 
