Requesting the meaning of a rucha

[satyajit B]

Dear Leaned Sirs

I request word by word meaning for the following mantra from Sandhyavandana, as well as its origin. The mantra is 

सस्रुषीः तदपसो दिवा नक्तं च सस्रुषीः |वरेण्यक्रतूरहमा देवीरवसे हुवे॥ 

It follows the Mantra, of six Richa-s, though may not be connected.

ॐ शं न्नो देवीरभिष्ठयष्टय  आपो भवन्तु पीतये॥ शं योरभिस्रवन्तु नः॥ १॥

I shall be obliged for your guidance.

Best regards
Satyajita,