Hi Nathaniel,

It would be helpful to see the ooetheca from multiple angles. The ooetheca of the Carolina mantis is differentiated from the chinese and european mantids mainly by shape. The Carolina mantis has a more slender and elongated ooetheca than those other two species. 

Also, those ooetheca may be empty. Mantids lay their eggs in fall, which overwinter and hatch in the spring. It's possible they already emerged.