BY K. M. JOHNSTON, F.L.S. 



63 



Shell depressed, lenticular Botellidfe, xlii. 



(f.) Shell oval shaped. 

 Interior with a shelly process Calytraeidse, xxiv. 



(g.) Shell depressed or ear shaped. 

 Shell depressedly turbinate, umbilicated Liotiidse, xli. _ 

 Shell ear shaped, thin, fragile, pellucid Naticidas, xxin. 

 Shell ear shaped, nacreous not perforated Stomatelhdee 



Shell ear shaped, nacreous perforated 



with holes Haliotidse, xlviii. 



(2.) Shell irregularly spiral. 

 Aperture rounded, entire, or with a 



longitudinal slit Vernietidse, xxix. 



(3.) Shell flat or simply conical. 

 Conical, curved anterior, margin notched 



or the apex perforated 

 Conical or depressed, neither notched 



nor perforated 

 Like Patella, but having a projection 

 formed over a siphonal groove 

 on right side 

 Shell small, translucent trigonal 



(4.) Shell multivalve 

 Shell composed of eight separate imbri- 

 cating plates 



Pissurellidse, xlix. 

 Patellida?, 1. 



Siphonariida?, lxvii. 

 Aplysiida?, lvii. 



Class SCAPHOPODA. 

 (5. ) Shell tube-like, tapering posteriorly 



Chitonidse, li. 

 Dentaliidoi, lxviii. 



(II.) MABTNE BIVALVES. 

 Class PELECYPODA. 

 (A.) Bivalves cemented to or contained within a shelly tube. 

 Shell either small, equilateral, cemented 



to the lower end of a shelly tube, 



umboes alone visible, as in Asper- 



gillum, or wholly contained within 



a tube as in Gasterochccna Gastrochsenidse, lxix. 



■(-8 J Bivalves not cemented or contained within a shelly tube. 

 (1.) Dorsal margin protected by one or more accessory valves. 

 Shell gaping at both ends, thin, brittle 



white, very hard. Borers Pholadidse, lxxi. 



(2.) Bivalves lacking accessory valves. 

 (a.) Two adductor impressions, nearly equal. 



Pallial line sinuated. 

 t Ligament external. 



