few neural spines are taller than the corresponding centra, but then decrease in height gradually. The tops of the neural spines, which are the thinnest parts of the bones, are straight, instead of being notched like Undorosaurus or Platypterygius australis. The ribs are shaped like a figure eight in cross section near their top ends, but this is less obvious closer to the bottom; such a morphology is typical among ophthalmosaurids, except for Acamptonectes and Mollesaurus. The dorsal ribs are around long, while the first few caudal ribs are only long. Forelimb and pectoral girdle In Arthropterygius, the scapula has a relatively straight blade that was broadened at its front end into a fan-like acromion process. This process is less prominent than that of Acamptonectes and Sveltonectes, instead being more similar to that of Undorosaurus, Platypterygius hercynicus, and Sisteronia. The scapula formed more of the glenoid than the coracoid; like Sveltonectes but unlike Undorosaurus, the glenoid does not extend onto the bottom face of the scapula. The de facto blade of the scapula was widest near the middle, and angled slightly downwards; like Acamptonectes but unlike all other ophthalmosaurids, the blade has a relatively uniform thickness along its entire length. The clavicle, which is not fused to other elements in the pectoral girdle, bears a thickened process on its frontal bottom edge which points towards the midline of the torso. This process is relatively short, square-shaped from the front, and bordered by a rim on its back edge. In most other ophthalmosaurids, this same process is more finger-like, although some specimens of Ophthalmosaurus have similar processes. The back part of the clavicle gradually narrows into a curved point, as in Ophthalmosaurus and Baptanodon. The coracoid is a kidney-shaped bone that is about as long as it is wide, compared to Undorosaurus, Nannopterygius, and Sveltonectes, where it is not as wide proportionally. Like Ophthalmosaurus, the coracoid bears a prominent notch on its front edge; it also bears a ridge on the frontal part of its midline, like Ophthalmosaurus and Acamptonectes, but unlike Caypullisaurus and Platypterygius australis. Its articular facets with the scapula and glenoid are clearly separate, as in Sveltonectes but not Acamptonectes. The former is only about 45% of the latter in length; this figure is 50% in Undorosaurus. There are two prominent processes on the humerus. The longer, less prominent, and more ridge-like of these is the dorsal process.