**First** **he** **failed** **to** **see** **the** **great** **structural** **difference** **between** **the** **penguins** (**which** **Illiger** **had** **placed** **as** **a** **group**, **Impennes**, **of** **equal** **rank** **to** **his** **other** **families**) **and** **the** **auks**, **divers** **and** **grebes**, **Pygopodes** - **combining** **all** **of** **them** **to** **form** **a** "**Typus** " (**to** **use** **his** **term**) **Urinatores**; **and** **secondly** **he** **admitted** **among** **the** **Natatores**, **though** **as** **a** **distinct** " **Typus** " **Podoidae**, **the** **genera** **Podoa** **and** **Fulica**, **which** **are** **now** **known** **to** **belong** **to** **the** **Rallidae** - **the** **latter** **indeed** (**see** **Cool**') **being** **but** **very** **slightly** **removed** **from** **the** **moorhen** (**q**.**v**.).

**The** **sixth** **order**, **Natatores**, **consists** **of** **all** **the** **birds** **that** **habitually** **swim** **and** **a** **few** **that** **do** **not**, **containing** 6 " **cohorts** ": **Longipennes** **and** **Pygopodes** **with** 3 **families** **each**; **Totipalmatae** **with** **I** **family**; **Tubinares** **with** 3 **families**; **Impennes** **with** **I** **family**, **penguins**; **and** **Lamellirostres** **with** 2 **families**, **flamingoes** **and** **ducks**.

**Iv**., **Boston**, 1885) **gave** **the** **Impennes** **independent** **rank** **equivalent** **to** **the** **rest** **of** **Carinate** **birds**; **M**.