【A/The series of + n 】主语根据A series判断.谓语是单数.若是【two series of +n 】谓语就是复数
总的说来：a/the series of +n 用单数形式的谓语动词
series of + n 用复数谓语动词
“a series of+名词”作主语时,动词用单数,
如：A series of pre-recorded tapes has been prepared for language laboratory use.已经为语言实验室准备了一系列预录的磁带.
同样的还有a kind of,a portion of等,这是习惯用法 .
至于第二句：
When Russell Wallace and Darwin independently proposed similar theories,Darwinhad already accumulated extensive evidence with which to support his ideas.
前面是说的【Russell Wallace and Darwin】,后半句是说【Darwinhad】,那么his到底是说他们俩人,还是【Darwinhad】,这里存在歧义.
因为his既可以解释为”他的“,也可以解释为”他们的“