How can I select this span element?

I am just starting with Selenium and now you need to select this element:

<span class=" close">Matrices</span>

This line of code returns null elements, so I assume this is not correct :-)

ReadOnlyCollection<IWebElement> matrixLink = driver.FindElements(By.PartialLinkText("Matrices"));

But I couldn’t find a suitable one other than Xpath, but it looks like this ( //*[@id=\"Navigation\"]/div[2]/div[2]/ul/li[7]/span) and it seems a little fragile for me?

EDIT : span has a class of "close". This is part of the menu, where there are 19 spans with the "close" class, so it is not a unique selector, unfortunately ....