NATUKAL HISTOKY SOCIETY. 81 



E. Dorsal tentacles not retractile into sheaths ; some are without tentacles. 



46. Mlidce. 



F. Gills non-retractile, forming only a half circle of few plumes 



44. Polyeeridce. 



P. Gills either retractile into one or more cavities or united by a web at 



base ; they form a complete circle or star 4S. Dorididce. 



G-. Broad oval in form ; f as wide as long 42. Doridellidce. 



Gr. Elongated, body itself narrow, some specimens seemingly broad when 



swimming by the spreading of wing-like expansions on the sides 



47. ElysiidcB. 



H. Shell with the whorls regularly in a single plane and not touching 



each other; ')^0.%^.it.C %.%%... }^\.(^..^.:]........7L Spirulidce. 



H. Dextral or right handed shells. (J.) 

 H. Sinistral ; the whorls in contact. (I.) 

 I. Shell ovate-globose, small, not over 5 long, transparent...<34. Limacinidw. 



I. Shell elongated, turreted, slender, less than 30 long 38. Triforidm. 



I. Shell large, over 100 long, with a produced anterior canal 



51. FaseiolariidcB. 



J. Operculated (nearly all marine univalves are operculated); aperture not 

 over one-half the area of the shell, usually much less than one-half. * (N.) 

 J. Non-operculated, or operculum very minute; aperture with neither a 

 canal nor notch at the anterior end. (K.) 



J. Non-operculated ; aperture with a canal at the anterior end....O.H^X. 



S.y.l^.':^.>.^5...1.^.S.S...tf^.^:<^...i.a..k>^^ 50. Pleurotomidw. 



K. Aperture over f the area and f the length of the shell ; spire distinct, 



pointed ; shell ear shaped 67. Natieidce. 



K. Aperture ^ the area or more and the full length of the shell. (M.) 

 K. Aperture less than ^ the area of the shell. (L.) 

 L. Aperture f to the full length of the shell ; spire distinct, in most cases 



flattened; inner lip with a single fold or smooth 38. Tornatinidce. 



L. Aperture about ^ tlie length of the shell ; shell globose, thin, fragile, 

 translucent ; outer lip very thin ; 20-25 long and wide. Shells of Janthina 

 fragilis in Janthinidre. Karely thrown on the beach. 

 L. Deep water species with the inner lip with no teeth but a strong fold ; 

 aperture about Mhe length of the shell ; spire conical ; whole shell 

 many whorled and spirally grooved with, in most cases, punctate stride ; 



12 or less long 57. Aetceonidce. 



It. Aperture A-| the length of the shell; inner lip with 2 or more teeth.... 

 48. Auriculidce. 



