In a brief respite from a quarter century of Puritan austerity, the Class of '33 embarks today on a four-day 25th Reunion embellished with straw hats, class ties, plastic badges, and special parking privileges, courtesy of the Cambridge Police Department.

Estimated to be the largest reunion in Harvard history, the 25th will run a week's gamut of luncheons, tours, concerts, wining and dining, and sports from swimming to golf--with social head-quarters at the Hasty Pudding-Institute of 1770.

University Open House Today

Today's events include a University Open House in the morning, facilitated by a regular shuttle service of buses to the Science Buildings, the Observatory and Union. The afternoon features a symposium at New Lecture Hall on Harvard after a generation, and the evening cocktails and the Pops Concert at Symphony Hall.

Members of the Class of '33 will also be treated to the first public exhibition of the Kronosaurus sea monster, a fossil skeleton of what was once the largest flesh-eating reptile in the sea. Reunionrs have been invited to a pre-public unveiling today. The exhibit will be open on general exhibition tomorrow, June 10.

Tuesday is Essex day-swimming, golf, tennis, softball, for the athletes; cocktails, a lobster dinner, and a diving exhibition for the more contemplative; and more cocktails, movies, and a sports dance to wind up the evening.

A series of panels on education and a class picture at 11:30 a.m. take up Wednesday morning, with the Harvard-Yale baseball game in the afternoon and a dinner dance in the evening. Thursday features an alumni parade, Commencement exercises, a boat trip, picnic lunch, and farewell tea.

Class of '33, the first class to spend its freshman year in the Yard, is dominated by educators, lawyers, and financiers; it has only one fisherman.