Most famous these depicted here is Metaspriggina which funnily enough is known from the Burgess Shale in what is now British Columbia around 513 to 505 million years ago being contemporary with Pikaia,
Less famous is Emmonsaspis which was discovered from the Parker Slate which dates to around 505 mya in what is now Vermont, which despite being a place of exceptional preservation akin to the Burgess Shale and being discovered 25 years earlier was all but forgotten as a valid source for fossils until 2021.
Even more obscure is Nuucichthys which is known from the Marjum Formation in what is now the House Range mountains of Millard County, Utah.
Lastly and most obscure is Zhongxiniscus known from, as you might guess by the name, the Maotianshan Shales of China 518 million years ago.
Top Row: Emmonaspis worthanella, E. cambrensis
Middle: Metaspriggina walcotti
Bottom Row: Nuucichthys rhynchocephalus, Zhongxiniscus intermedius
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https://www.amazon.com/dp/B0DX5PBN9V
and the second Book here
https://www.amazon.com/dp/B0FTGL2MVT