[1] John Campbell Merriam (1902) described it as a new species of Shastasaurus, S. perrini, honouring Professor James Perrin Smith as discoverer, based on holotype UCMP 9119.

Merriam (1938) independently erected Perrinosaurus to replace Delphinosaurus, but this is a junior objective synonym.

[3][4] The long-snouted head is small in comparison with the rest of the body, as in basal ichthyosaurs such as Mixosaurus and Cymbospondylus.

[5] The tail is sharply turned downwards, in common with more advanced ichthyosaurs, with a small vertical fluke.

The phalanges (digit bones) are circular and widely spaced, giving the flipper a round appearance.