REPORT ON THE MOLLUSCA 

 Cuspidariids 

 Clavagellidae Poromyidoe 



Pholadacea Aiiatinacea Tellinidre 



39 



LuciniJaj 



Ostracea 



Couchacea 



Pectinacea 



Submytilacea 



Mytilacea 



Trigoniid* 



Solenoinyidae 



\ 

 ArcidsB 



Nuculidae 



In tliis table the branch proceeding from JMytilacea to Ostracea corresponds to the 

 Dysodonta of Neumayr ; the branch from Submytilacea to Tellinidfe and Lucinidse 

 represents Neumayr's Heterodonta, and the Myacea with the two branches which rise 

 from them are his Desmodonta. 



It will be noticed that the above table differs in several points from that of Professor 

 Neumayr (loc cit., p. 413). In fact, I regard his Palseoconcha as arising from the 

 Taxodonta (Arcacea), rather than as giving origin to them. It is possible that these 

 Palseoconcha represent the origin of the Solenomyidis. 



And again, I regard the Trigoniidse as the direct derivatives of the Arcacea. The 

 nature of their mantle, of their foot, and of their gills, which consists each of two plates 

 of filaments,' afford strong evidence in favour of this interpretation. 



As to the Monomyaria (Ostracea and Pectinacea) and the Heteromyaria (Mytilacea), 

 I am in entire agreement with the opinion of Neumayr, which is shared, I believe, by all 

 malacologists, that the first are derived from the second, of wdnch they merely constitute 

 a " sedentary " specialisation. The Heteromyaria find their origin in the Arcacea, 

 through forms belonging to the Aviculidae, and more especially to the Pterinein^e (such 

 as Macrodon and Pterinea). 



As regards the Desmodonta and Heterodonta, it will be seen that I do not regard 



1 Huxley, Description of the animal of Trigonia, Proc. Zool. Sec. T.mJ., 1859, p. 31. 



