Sentence:  For four of the six ( the anaconda and the amethystine python cannot be included for lack of data ) there is also a correlation between size at maturity and maximum length , the boa constrictor <WSD>being</WSD> the smallest and the Indian python the next in size at the former stage . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)