4 BEITISH MARINE TESTACEOUS MOLLUSCA : 



SYNOPSIS OF THE FAMILIES AND GENERA OF THE BRITISH TES- 

 TACEOUS ACEPHALA, GASTEROPODA, AND CEPHALOPODA, 

 DISTRIBUTED IN SIX DIVISIONS, ON THE BASES OF SEXUAL 

 ORGANIZATION. 



First Division. 



ACEPHALA PALLIOBRANCHIATA. 



Hermaphrodita, sine concubitu. 

 TEREBRATULID.E Hypothyris. 



Terebratula. 



Argiope. 

 CRANIAD^E Crania. 



Second Division. 

 ACEPHALA LAMELLIBRANCHIATA. 



Hermaphrodita, sine concubitu. 

 * Mantle open, no tubes. 



ANOMIAD.E Anomia. 



PECTINID.E Pecten. 



OSTREAD.E Ostrea. 



** Mantle open, no siphonal tubes or sessile. 

 MYTILID.E Mytilus. 



Dreissena. 



Modiola. 



Crenella. 



Pinna. 



Avicula. 

 UNIONID.E Unio. 



Anodon. 



*** Mantle open, tubes sessile or short. 



ARCADE Area. 



Pectunculus. 



Nucula. 



Leda. 



Galeomma. 



Lepton. 



