Mariella worthensis
Heteromorph
Lower Cretaceous (Cenomanian)
Pawpaw Formation
Glengarten, Fort Worth, Texas, USA.

18mm heteromorph ammonite.

Cephalopod.

Mariella is an ammonite genus that lived during the last part of the Early Cretaceous (Late Albian) and the first part of the Late Cretaceous (Early Cenomanian).  It has been found in many parts of the world (North America, Europe, Africa, Australia, and New Zealand).  In the Del Rio Clay of Texas it can be found pyritzed.

Affordable example of a heteromorph ammonite. Nice color.