श suffix is implied for verbs - लिप्,विद्,धृ with -णिच्,पॄ,विद्(of चुरादिगण),उद् prefixed एज्,चित्,साति(सौत्र),सह्. For example, लिम्पः,विन्दः etc. {exception}. Notice that क would be implied in non-prefix context - प्र लिप् क - प्रलिपः (notice how श् introduces the nasal sound).