ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
583 
himself that the complication of the gill indicates the degree of speciali- 
zation of the different groups of Laraellibranchs, and he offers the 
following classification. 
, Septibranchiata 
Pholad$cea Anatinanea 
Cai:diacea """Alyacea 
" "VjeUeracea 
TeUinacea 
Submytilacea 
Eulamellibranchiata 
Ostrseidse 
; Avicijlidse Pectinidae 
Pseudolamellibranchiata 
My.tilidae 
/ Trigoniidae 
Arcildse 
Anomiidae^^ 
Filibranchiata 
Solei^omyidae^^j 
Nuculidae 
Protobranchiata 
If we compare the Lamollibranchs with other groups of the Mollusca 
we find that they are much more specialized than the Amphineura, very 
different from the Cephalopoda, by no means so allied to the Scaphopoda 
as has been suggested by Lacaze-Duthiers, but showing many points of 
resemblance to the Rhipidoglossa. Of these last the least specialized 
show a marked symmetry of gills, osphradia, auricles, and renal organs ; 
the edge of the mantle is free ; some archaic forms, such as Haliotis , 
have well-developed hypobranchial glands ; Fissurella and Trochus 
turritus have a crystalline style. The structure of the gills in di- 
branchiate Rhipidoglossa is absolutely similar to that of the Nuculidae 
and Solenomyidae. The crossing of the ventricle by the rectum is 
found only in Lamellibranchs and some Rhipidoglossa ; pericardiac 
2 t 2 
