OF MOLLUSCA. 135 



Order II. Scutibranchiata. 



Gills consisting of two series of lamellae, forming one or two series 

 over the back of the neck or under the edge of the mantle round 

 the foot. Animal hermaphrodite, self-impregnating? Shell spiral 

 or symmetrical, conical. Rectum often traversing the heart. 



Synopsis of Suborders. 



I. Biphidoglossa. Teeth transparent, glass-like, in numerous 

 longitudinal series ; the central 5*1*5, variable in form ; 

 lateral very numerous, more slender, curved at the tip. 



I. Scutibranchia. Gills in a spiral line on the left side of the gill- 



cavity. Body, shell and operculum spiral. Eyes pedicelled. 



* Sides of the foot without any fringe or tentacles. Shell not 

 pearly. Central teeth unequal. 



** Sides of the foot with a fringe furnished with beards. 

 Shell pearly. Central teeth equal, similar. 



II. Schism atobranchia. Gills in two plumes on left side of the 



gill-cavity, on each side of mantle-slit. Body and shell spiral. 

 Foot fringed and bearded. Eyes pedicelled. Central teeth very 

 unequal, large, dissimilar. 



III. Dicranobranchia. Gill s in t wo symmetrical dorsal plumes. 

 Body and shell not spiral. Foot slightly bearded. Eyes sub- 

 sessile. Central teeth of two kinds, inner small, similar, outer 

 large, dissimilar. 



II. Heteroglossa. Teeth pellucid, in Jive to eight longitudinal 

 series, variable in form, the larger ones with opake black tips. 

 Foot without any lateral fringe. Shell symmetrical. 



IV. Cirrhobranchia. Gills tufted, on back of neck. Body 

 elongate-conical. Shell tubular, with an apical opening. 



V. Cervicobranchia. Gills lamellar, in a single series on the side 



of the gill-cavity on the back of the neck. Shell conical, sym- 

 metrical. 



VI. Cyclobranchia. Gills lamellar, on the inner surface of the 

 mantle, forming a more or less complete ring just beneath the 

 margin. Shell conical, symmetrical. 



VII. Polyplacophora. Gills in two lamellar series on each side 

 of the hinder part of the under side of the mantle-edge. Shell 

 formed of eight imbricate valves. 



