This article analyzes manuscript 308 of the Book of Psalms from the Holy Trinity-St. Sergius Lavra collection stored in the Russian National Library. It was first studied by the Russian linguist Fyodor Buslaev in the 19th century. His conclusions about the nature of the spelling patterns and ornamentation of the manuscript are confirmed at the textual level. The paper identifies the sources of the liturgical terminology and the versions of the New Testament readings in the manuscript.