Dwight describes Larus cachinnans Yellow-legged Gull from p.202-207. Within this form appears to be both Caspian Gull cachinnans and Mediterranean Yellow-legged Gull michahellis as known to today's gull watchers. The pages below contain the summary of Dwight's cachinnans.

The following points are of interest:

• There are two large mirrors [on P9 and P10] in typical specimens.
• Its voice is unlike argentatus but somewhat resembles that of marinus.
• It cannot be a Herring Gull because of the yellow legs and feet and white head in winter.
• It cannot be a Lesser Black-backed Gull because of the extensive white wing pattern.
• It may therefore be considered a full species although intermediate between the two.
• As the western limits of its range are approached:
• The white in the wing pattern diminishes sometimes to grey;
• Only one mirror is found;
• Some specimens approach atlantis although they usually have longer [pale] tongues on more of the primaries.