Answer: Taenia saginata proglottid
As many of you have pointed out, the identification can be made based on the presence of more than 13-15 primary lateral uterine branches on each side of the uterine stem. When counting branches, remember to count them as they come off of the uterine stem rather than at their terminal ends, since the latter will give you a falsely elevated count. Also, remember to only count on 1 side of the uterine stem to get your total. I've highlighted the uterine stem and a few of the primary branches below. Although it's sometimes hard to figure out which are primary vs. secondary branches, I believe we still have at least 13 primary branches in this case (using a conservative estimate).
Of note, Taenia asiatica has a very similar appearance and therefore obtaining a travel history is important in formulating your differential. In my lab, the primary concern is ruling our Taenia solium, since the infected individual and his or her contacts may be at risk for cysticercosis from eggs being shed in the stool. In comparison, the eggs of T. saginata and T. asiatica are not infectious to humans and do not cause cysticercosis.