a kind of 后面接的名词即使是可数名词，通常也用单数，一般不用复数。如：

This is a kind of new car. 这是一种新型汽车。

The waltz is a kind of ballroom dance. 华尔兹是一种交际舞。

There is a kind of strange animal in the zoo.  动物园里有一种奇怪的动物。

The heart is a kind of natural pump that moves the Blood around the body. 心脏是一种天然唧筒，使血液在体内循环。

There is a kind of tree in the garden which flowers once every two years. 院子里有一种每两年开一次花的树。