RANGE OF FAMILIES IN TIME. 



125 



lY. EANGE OF FAMILIES IN TIME. 



Systems ) 

 of Strata, j 



Cambrian. 



Silurian. 



Devonian. 



Carbonif. 



Permian. 



Trias. 

 L. Jura. 

 U. Jura. 

 i;. Cret. 

 U. Cret. 



Eocene. 

 Miocene. 

 Pliocene. 

 Eecent. 





Argonautidse 



Teuthidee— Sepiadee 































Atlantidffi — Hyaleidae 



Strombidee — ^Buccinidee 



ConidcB— Volutidae 



Naticidee— Calyptrseidse 



PjTamidellidBe 







— 

































Fissurellidee— TornatellidEe 



Neritidge— Patellidse 



































"RnlliVltP 











HelicidEe — ^LimacidEe 



Limnaeidee — ^Melaniadae 



Auriculidse — Cyclostomidee 











— 









Terebratulidse 





















CraniadEe — Lingulidse 































Arcadse — ^Trigoniadee 























, 





















Cardiadse — Lucinidee 













Cj^rinidae — ^Anatinidae 

















Veneridae — Tellinidse 



IVIactridEe 









— 



- — 









Gastrocheenidee — Pholadids 















_ 



Distrilnition of Families of Shells in Time. — Employing the term 

 "families" for natural groups of genera, and adopting the 

 smallest possible number of them, we find that sixteen, or 

 nearly one-fifth, range through all the geological systems. Only 

 seven have become extinct, viz. : — 



Belemnitidse. 

 Ammonitidje. 

 Ortlioceratidae. 



Spiriferidse. 



Orithidse. 



Productidse. 



Hippuritidse. 



