Ian Redmond recently opined that tarsiers, which can swivel their heads 180o, look like the creation of a Hollywood special-effects team. They are intermediate between lemurs and lorises on the one hand and monkeys and apes on the other. Tarsiers are easily overlooked in surveys of primate placentation. None of the accounts are recent so they do not readily pop up in literature searches. Hubrecht’s own description can be hard to track down so follow this link and scroll down to Appendix B. A more accessible interpretation of the same material is in J. P. Hill's classic review.
The exchange area of the tarsier placenta is reminiscent of that in Neotropical primates, with the villi connected by trabecula.
It was on the basis of placentation that Hubrecht suggested tarsiers belonged with monkeys and apes in what are now referred to as haplorrhine primates. This led to a spirited debate in the pages of Science and American Naturalist with Charles Earle, curator of fossils at the American Museum of Natural History. Earle wanted to keep tarsiers with lemurs and lorises (strepsirrhine primates).