* Lamont Library will stay open until midnight, Monday through Friday, starting next Monday.

* Emelio Fontana of Brazil, a member of the International Seminar, will play recordings of music from his country at the Recorded Music Hour in Matthews 5, Sunday, 2-5 p.m. Fontana will comment briefly about the program, which will include both classical and folk selections and recordings of percussion instruments unknown in this country.

* Saturday's concert from 3-5 p.m. will be Telemann's Concerto in D major for Trumpet, Strings and Continuo and Concerto in D major for Trumpet, Two Oboes and Continuo; Boyce's Symphoiny no. 2 in C major and Symphony no. 4 in F major; Locatelli's Concerto no. 2 in C minor for Violin, Opus 2; Schuman's Carnaval; and Stravinsky's The Fairy Kiss, complete balled.

* The Claremont Quartet will play to night in Sanders Theatre at 3:30 p.m.: Beethoven's Quartet in G major, Opus 18, no. 2; Quarteet in D major, Opus 18, no. 3; and Quartet in B fiat major, Opus 130, with Grosse Fuge.

* The Busch-Reisinger Museum presents recorded music Monday through Friday from 1-2 p.m. in its garden (Kirkland St. and Divinity Ave.). The public is Divinity Ave.), The public is invited free of charge, and lunches may be brought. Each Wednesday the selection is related to a work of art. Next week: Mozard, Cost fan tutte; Hindemith, Mathis der Maler (Wed.); Schuller's Seven Studies on Themes by Paul Klee (Wed.): Stravinsky's Apollon Musagete; and Schubert's Octet.

* Another square dance will be held at the Union--Tuesday, 2:20 p.m.

* A dance for graduate students at the Summer School wil be at the Union, 8:20 p.m. Wednesday.

* The Old North Church Guild for the Arts presents a series of free concerts Wednesdays at 8 p.m. during the summer. Next week: The Old North Singers will perform seven madrigals, six chansons by Rilke, and three chansons by Charles d'Orleans.

* The Harvard Summer Players reminds Summer School students that they are welcome to work in the Loeb Drama Center, especially if they have experience in costumes, properties, or set construction.

* A dormitory dance--for residents of Kirkland, Massachusetts. Lionel, Quincy, Dunster, and Matthews South and their guests--will be held tomorrow at the union, 8:30 p.m. "The oriental Teahouse" has been chosen as the theme will Chinese lanterns, posters, and geisha girls serving refreshments. Music will be provided by George Graham and his Orchestra will intermission entertainment by Arma Schefrin, of Widener Quadrangle song-fest fame.

* The Boston Naval Yard announces a series of Monday night track meets, open to any and all amateur athletes.