MARY ANN UMSTEADUmstead-MackellMr. and Mrs. Edwin A. Umsfcead of Fountainville announce the engagement of their daughter Mary Ann to Dr. Thomas E. Mackell of Penllyn.Dr. Mackell is the son of Dr. and Mrs. James V. Mackell of Huntingdon Valley and Stone Harbor, N.J.Miss Umstead graduated from Allentown Hospital School of Nursing and will attend Thomas Jefferson University. She la a registered nurse employed at Doyleatown Hospital.Dr. Mackell is a graduate of Georgetown University and Jefferson Medical College. He is an orthopaedic surgeon on the staff at Doyleatown Hospital.A Dec. 4 wedding is planned.