202 On the Primary Divisions of the Bracliio]iods. 



and in the other ( CUstenterata) none. Witli these characters, 

 be it remarked, are generally coincident structural modifica- 

 tions of the hinge of the shell — the species with an anal aper- 

 ture having an inarticulating hinge generally, and those with- 

 out the anal apertui-e having a more or less interlocking one. 

 On one or other (or both) of these characters (and witli coor- 

 dinate ones) these groups have been repeatedly recognized, 

 first by Owen, and then by Bronn, Huxley, and others. Owen, 

 it is true, vigorously opposed the assertion that any forms had 

 a csecal intestine ; but the groups he recognized were, as to 

 their constituents, exactly equivalent to the Tretenterates and 

 Clistenterates, although based only on the simple or interlock- 

 ing hinge and relative proportions of the viscera and brachia. 

 All other naturalists who have adopted the groups, however, 

 have especially recognized the perforation or non-perforation 

 of the intestinal tube in their diagnoses ; and the groups have 

 been adopted by the following naturalists, viz. : — 



I. 



Lyopomata, Owen, Encycl. Brit. 8th edit. vol. xv. p. 301, 1858 *. 

 Pleiiropygia sen Ucardines, Bronn, Klass. u. Ordn. Thierreiehs, p. 301, 



1862t. 

 Ina7i,iculata, Huxley, Int. Class. An. p. 116, 1869 J. 

 Lyojmmata, Gill, Arr. Fam. Moll. p. 26, 1871 : Dall, Am. Journ. Conch. 



vol. vii. p. 71, 1871. 

 Tretentei-ata, King, Ann. & Mag. N. H. (4) vol. xii. p. 15, 1873. 



11. 



Arthropomata, Owen, Encycl. Brit. 8th edit. vol. xv. p. 336, 1858 §. 

 Apygia seu Testicardines, Bronn, Klass. u. Ord. Thierreiehs, p. 301, 



186211. 

 Articulata, Huxley, Int. Class. An. p. 116,18691]. 

 Arthropomata, Gill, Arr. Fam. Moll. p. 25, 1871 ; Dall, Am. Journ. 



Conch, vol. vii. p. 60, 1871. 

 CUstenterata, King, Ann. & INIag. N. H. (4) vol. xii. p. 15, 1873. 



The conclusions of Prof. King (he being unaware of the 

 labours of his predecessors) are noteworthy, as being inde- 



* " Shell- valves inarticulated, and, save in the annectant family Cra- * 

 niadce, subcalcified ; viscera occupying one half, brachia the other half, of 

 the shell-cavity " (I. c. p. 3.30). 



t " Nahrungskanal (in den fossilen Sippen nur vermuthungsweise) 

 lang, gewunden, durch einen After (rechterseits ?) ausmiindend," &c. 

 (/. c. p. 301). 



X " The intestine terminates in an anus on one side of the body " (/. c. 

 p. 116). 



§ " Shell-valves articulated, calcareous ; viscera occupying one third, 

 brachia two thirds, of the shell-cavity " ( /. c. p. 336). 



Ij " Nahrungskanal (bei den ganz fossilen Familien nur vermuthungs- 

 weise) mit einfachem abwarts gebogenem blind endigendem Darm- 

 Anhange (Afterlose)," &c. {I. c. p. 301). 



f "The intestine ends in a blind sac '' (I. c. p. 116). 



