ORDERS AND FAMILIES. 89 



SCYLL/EID.E. Body oblong, compressed ; two large, foliated cerata, with 

 branchial appendages on the inner side ; no tentacles. Scyllaa, 600. 



TRITONIID.E. Body long ; two rows of unequal arborescent cerata, 

 Tntonia, 602. 



PTEROPODA. Plate xxx. Nos. 583 to 585. 



CAVOLINIID^. Fins large, shell a cone, angular or circular, very thin, 

 ridged lengthwise or spinous ; five ridges in front and one at back. 



Clio, 584. 



CLIONID^E. Body long, angulated behind, no shell. Clione, 585. 



LIMACINID/E. Fins very large, shell spiral, thin and fragile, translucent ; 

 whorls five in number, tumid, the last more than half the shell ; 

 umbilicus small. Spirialis, 583. 



TECTIBRANCHIATA. Plate xxx. Nos. 550 to 582. 



;. Shell spiral, solid, entirely covering the animal ; spirally 

 striated; spire generally prominent, pillar with ridge-like fold con- 

 tinued within the spire; suture well marked. Action, 550. 



. Shell arched, flattened, slightly convolute at smaller end 

 which is thickened by a projection ; mouth extending whole length of 

 shell ; spire short and terminal. Aplysia, 577 to 579. 



BULLION. Shell convolute internal or partly internal ; spire hidden or 

 nearly so, mostly short ; mouth extending the whole length of the 

 shell or nearly so. Bulla, 565 to 567 ; Acera, 568. 



. Shell internal, thin, slightly spiral ; spire small and truncated; 

 mouth large and open ; pillar sharp-edged, flexuous and visible 

 throughout. Philine, 569 to 576. 



PLEUROBRANCHID^. Dorsal region protected by a covering or shell, 

 Pleurobranchus, 580 to 581. 



RUNCINID^;. No shell. Runcina, 582. 



SCAPHANDRID.E. Shell oval, spirally striated, external, covering all or 

 nearly all the animal ; spire hidden ; mouth extending whole length 

 of shell, contracted behind, expanded in front ; pillar smooth and 

 with a blunt edge. Scaphander, 558, 559 ; and CyUchna, 560 to 564. 



TORNATINID^;. Shell cylindrical or globular, covering the animal, spire 

 truncated ; whorls keeled ; mouth extending whole length of shell, 

 expanding in front; small fold at base of pillar. Tornatinus, 551 to 557. 



PrOSObranchiata. (GASTROPODA.) Plates xxi. to xxix. 

 Nos. 319 to 549. 



ACICULID^. Shell small, cylindrical, thin, with long blunt spire; mouth 

 oval; umbilicus straight ; operculum horny. Acicula, 398. 



Shell patelliform ; crown close to front margin; internal 

 border distinctly marked. Tectura, 319. G 



