अन्वयः

संविशद्भि: preparing to lay down, महाद्रिकूटप्रतिमैः as huge as mountain peaks, बहुभिः by many, प्लवङ्गमैः by monkeys, भृशम् greatly, सन्नादितनिर्दरान्तरः the sound that came from inside the cave, सः that, महीधरः mountain, नदद्भि: by the thundering, जलदैः with clouds, इव like, उल्बणैः stormy clouds, बभूव appeared.

Summary

While the numerous monkeys, resembling peaks of high mountains were roaring, it resounded through the mountain caves. It was like the sound of the stormy thunderclouds.इत्यार्षे श्रीमद्रामायणे वाल्मीकीय आदिकाव्ये किष्किन्धाकाण्डे पञ्चपञ्चाशस्सर्गः॥Thus ends the fiftyfifth sarga in Kishkindakanda of the first epic, the Holy Ramayana composed by sage Valmiki.

पदच्छेदः

बभूव	बभूव (√भू लिट् प्र.पु. एक.)
संनादितनिर्झरान्तरो	संनादित (√सम्-नादय् + क्त)–निर्झर–अन्तर (१.१)
भृशं	भृशम् (अव्ययः)
नदद्भिर्	नदत् (√नद् + शतृ, ३.३)
जलदैर्	जलद (३.३)
इवोल्बणैः	इव (अव्ययः)–उल्बण (३.३)