112 GEODIA MESOTRIAENA. 



DIFFERENCES BETWEEN THE THREE VARIETIES OF GEODIA MESOTRIAENA. 



praeoscular cavities, differently shaped small strongylosphaerasters, and much 

 smaller megascleres and choanosomal oxyastons. Geodia brevicma also has much 

 smaller megascleres; this species is also distinguished from G. mesotriaena by 

 its minute, dermal anaclades and the thickness of tiie clades of the large ana- 

 triaenes. The species most nearly allied to G. mesotriaena are G. mesotriaenella 

 and G. ovis. Of G. mesotriaeriella there is only a small specimen in the collec- 



