The Singer Apollo was the first Singer safety bicycle with wheels of equal size, introduced in 1887. It was built until 1891-1892. To confuse matters, they also had an ordinary bicycle called Singer Apollo.
The 1891 Singer catalogue shows two models of the Singer Apollo safety. The simpler version had a socket head, which can be identified easily by the spring under the head tube.
Then, there was the 'special Apollo' which had a ball head, the Singer patent steering lock and it was lined. As a consequence: the normal Apollo was not lined?
I have pictures of tree different Singer Apolle safeties on my website. The first you can see here on this page. It has the socket head. It was sold in 2014 at Bonhams auction in London. Serial number is XX796. Without the complete serial number, it's hard to say when it was built. Last three digits of the serial number are stamped on top of the front fork. Don't look at the lamp, it's from the 1920's. Saddle support is supposed to point forward, like visible in de illustration.
The second is also the simple model, but some details are better visible. I photographed it in the Zweidrad museum in Neckarsulm in Germany. Click here to see the pictures.
The third is a later 'luxury' model, with ball head and steering lock. You can see its a later model from the single rubbers in the footrests. The older models (I estimate until late 1890) had two rubbers. Click here to see the later model.
So here's the pictures of the bicycle sold by Bonhams: