Processes interloan requisitions for library material between area/branch libraries and the main library; charges and discharges library material to users; examines collections of books, films, periodicals, and so forth to weed material for purpose of discarding due to obsolescence; inspects books for damage; lists overdue library material and completes overdue notices for notifying patrons; performs filing or shelving tasks involving the use of the Dewey Decimal Classification System and alphabetical filing systems beyond the initial letter of a subject or topic. The Principal Library Assistant, under general direction the Supervising Library Assistant, performs technical and/or paraprofessional duties of considerable difficulty in one or more of the functional areas of librarianship; and does other related duties as required.in order to perform day-to-day paraprofessional work directly related to the acquisition, organization, and distribution of library materials on the Bookmobile, including all aspects of circulation, evaluation and selection for weeding, processing of new books, organization of shelves and re-shelving, and managing holds.