IV. GASTEROPODA: PROSOBRANCHIA. 



379 



BRANCHIA. Two ctenidia (fig. 372), shell with marginal slit or with 

 holes corresponding to an anal notch in the mantle; auricles and ne- 

 phridia paired; heart traversed by intestine. FISSURELLID^, keyhole lim- 

 pets; shell conical, with apical opening. HALIOTID^E, abalones; shell 

 weakly spiral, flat, with a series of holes. Haliotis* (fig. 362, B). AZYGO- 



Fio. 374. American Pectinibranch gasteropoda. (From Binney-Gould.) A, Crepidula 

 fornicata; B, Lacuna vincta; C, llyanassa obsolete, ; D, Littorina palliata; E, L. 

 litorea ; F, Urosalpinx cinerea ; G, Purpura lapillus ; H. Buccinum undatum ; I, 

 Lunatia heros. 



BRANCHIA. One ctenidium, but two auricles. TROCHID^E, operculum 

 liorny ; Trochus, Margarita* TURBINID^E, top shells; operculum calca- 

 reous. Turbo, Phasianella. 



Sub Order II. PECTINIBRANCHIA (Monotocardia, Ctenobranchia). 

 ^Ctenidium unipectinate, osphradium well differentiated (fig 365), intestine 



