This fine structure dedicated to insurance was built at Locust and Sixth streets; it was alternatively named the St. Louis Life Insurance Company Building and the Equitable Building (after its main tenants). The building was constructed in 1871, according to Emporis, and has subsequently been demolished. At one time it held the main offices for the Missouri Pacific Railroad. It also was graced with multiple statues along its roofline that were intended for use on the Eads Bridge; this were removed some time before 1886.
The two sepia tone illustrations are from The Great South: A Record of Journeys by Edward King (1875) (freely available online from UNC-Chapel Hill [here]). King was quite smitten with St. Louis, remarking on its "continental" flavor that derived from the brown tinge on buildings that came as a result of coal burning.
A later view of the building without the rooftop statues, from Commercial and Architectural St. Louis by George Washington Orear (1888). Notice the horsedrawn trolley line.