What trilobites come closest to Bathynotus in ventral structure?
While no trilobites exactly match the lost or greatly reduced rostral plate of Bathynotus, among trilobites with conterminant hypostomes bearing small rostral plates there are two examples in which the rostral sutures converge anteriorly. The first example is in the Redlichiida, in the Emuelloidea. The ventral structure of the Australian emuellid Balcoracania dailyi is shown below. The rostral plate (pink) is not fused with the hypostome (orange), but bears a functional suture. The two connective sutures initially converge anteriorly, then diverge to meet the dorsal sutures along the anterior margin. . In the image below, the dorsal facial sutures are shown as dotted red lines, and in solid red lines are the connective sutures on either side of the rostral plate (pink). The hypostome is attached to the rostral plate by a functional transverse suture. The rostral plate of Balcoracania is narrower than the hypostome. The explode view of the hypostome and rostral plate, librigenae and cra
