A second addition to the writings on reptiles? (4)
I believe the answer is:
asps
'reptiles?' is the definition.
(asp is a kind of reptile)
'a second addition' is the wordplay.
'second' becomes 's' (common abbreviation).
'addition' becomes 'ps'.
'a'+'s'+'ps'='ASPS'
'to the writings on' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for asps that I've seen before include "poisonous things" , "Poisonous snakes" , "Pass (anag)" , "native Africans?" , "Pass among snakes" .)