-ASPIDOBRANCHIA. FISSURELLAD#. 211 
ORDER VII. ASPIDOBRANCHIA. 
Scutibranches Cuvier. 
Branchia & foliis plurimis efformata, sub testa posita. 
Testa exterior, non operculata. Sexus androgynus. 
Branchia formed of many leaves, placed beneath the shell. 
Shell exterior, not operculated. Sex androgynous. 
Synopsis Familiarum. 
Fam. 1. FissurELLADE&. Testa clypeiformis, conico-ele- 
vata aut depresso-conica, subtis cava; vertice perforato ; fora- 
mine ovato vel oblongo. 
Fam. 2. EmarGinuLtap&. Testa conico-elevata, anticé 
fissa; vertice recurvo. 
Fam. 3. Caputipa. Testa conica, integra. 
FAMILY I. FISSURELLADZ. 
Testa clypeiformis aut depresso-conica ; vertice perforata ; 
foramine ovato vel oblongo. 
Animal: caput et collum libera. Os rostriforme, retractile, 
maxillis nullis. Yentacula duo, conica, oculis ad basin exter- 
nam, Pallium lateraliter dilatatum, intus teste marginem 
undique impositum, subtus branchias ferens, extra testam semper 
prominulum. Branchie duze, superné pectinatze, é cavitate 
branchiali utroque latere colli prominentes. Pes latus, ovalis. 
Anus ad medium colli basis exeuns. Cor supra collum locatur. 
Cerebrum circa collum nervorum ramos angustos anticé et pos- 
ticé mittens, et a circuli parte inferiore rami duo ad viscera et 
pedem descendunt. 
