* Law of Faunal and Floral Succession: This law states that fossils found in different layers of rock (strata) represent organisms that lived at different times in Earth's history. Basically, the deeper the layer, the older the fossils.

* Shelled Animal: This suggests the fossil is likely from a marine environment, as many shelled animals live in oceans.

Most Likely Next Fossil: Given this, the geologist would most likely find fossils of other marine organisms from the same time period. These could include:

* Other types of shelled creatures: Clams, snails, trilobites, etc.

* Fish fossils: Depending on the age of the rock, the geologist might find bony fish, sharks, or even extinct fish types.

* Marine plants: Fossils of seaweed, algae, or other sea plants are possible.

Important Note: The specific type of fossils found will depend on the age of the rock and the specific environmental conditions that existed at the time.