RANGE OF FAMILIRS TN TIME. 



241 



" The same method of tabulation applied to families, that is, 

 to groups formed of related genera, shows that the extinct 

 families are relatively few in number. Among the reptiles, on the 

 eontrar}-, a large number of families and even several orders no 

 longer exist (Dicynodonts, Labyrinthodonts, Enalliosaurians, 

 Dinosaurians, etc.). The invertebrata, consequent!}'', have varied 

 less than the vertebrata. 



" Woodward, who has prepared the following table, indicates 

 only seven extinct families : Belemnitidse, Ammonitida?, Ortho- 

 eeratidtie, Spiriferidie, Orthisidge, Productidse., Hippuritidse. It 

 is evident that this list might be lengthened, but it can be said 

 in general that the important fossil types of mollusks which no 

 longer exist are relatively few in number. 



RANGE OF FAMILIES IN TIME. 



Systems 

 of Strata. 



a s 



a 



:; y: ;5 o i( 



.5 1-5 '^ O -^ 

 H v4 & ^q P 



Argonantidse, . . 

 Teuthidffi — Sepiadse, 

 Belemnitida3, . . . 

 Nautilidse, . . . 

 Ammonitidse, . . 

 Orthoceratidae, . . 



Atlantidfe — Hyaleidse, . . 

 Strombidse — Buccinidse, . . 

 ConidirB — Volutidae, . , . 

 Naticid^ — Calyptrseidse, 



Pyramidellidse, 



Cerithiadae — Littorinidse, . 

 Turbinidse — lanthinidse, . , 

 Fissurellidse — Tornatellidse, 

 Neritid£e — Patellidse, . . . 



Dentaliadas, 



ChitonidfE, 



BullidfB, 



Helicidas — Limacidse, . . . 

 Limna^idae — Melaniadse, . . 

 A-uricnlidse — Cyclostomidoe, 



Terebratulidfe, 



Rhynchonellidse, .... 

 Spiriferidee — Orthidse, . . 



Productidffi, 



Craniadse — Lingulidfe, . . 



w S S « 



16 



