ARCHEROPS, A NEW ANNECTENT HIPPOSIDERID GENUS (MAMMALIA: MICROCHIROPTERA) FROM THE AUSTRALIAN MIOCENE

The toothrows are slightly convergent anteriorly. The deep, broad V-shaped indentation that marks the palate's junction with the premaxillae extends posteriorly to the level of the M2 metacone. The palate midline and posterolateral indentations extend posteriorly to approximately level with the M3 protocone. Maximum width of the palate occurs at M3. Palatal foramina are scattered and poorly developed.

The nasals are divided by a median septum that is bordered ventrally by the dorsal palate and dorsally by the nasals (anteriorly) and cribriform plate (posteriorly). Lateral development of the mesethmoid plates results in separation of the ventral respiratory passages from dorsal and lateral olfactory chambers. The median septum is only slightly swollen throughout its length; it carries a duct that exits beyond the posterior extent of the vomer. The vomer does not extend posteriorly beyond the palate.

Between the orbital fossae, the braincase narrows markedly. The point at which the two supraorbital crests unite (i.e., where the sagittal crest originates) is posterior to the point of narrowest constriction. The palatines and pterygoids are normally developed. The sphenoidal bridge is broad anteriorly, constricted posteriorly. In ventral view, the sphenorbital fissure, which is long and oval, is exposed posteriorly and is separated from the relatively small optic foramen by a narrow bony splint. Pterygoid processes occur at a point approximately midway along the sphenorbital bridge. These processes have a secondary flange directed posteroventrally.

Immediately anterolateral to the sphenorbital fissure is a relatively large foramen that drains the anterior transverse sinus. Posterodorsal to the postpalatal foramen is the small sphenopalatine that leads into the posteroventral part of the nasal cavity. Posterodorsally and medially, several small foramina open into a long, curved, shallow groove that leads posterodorsally from the postpalatal foramen to the optic foramen. Dorsally and medially again is a deeper, shorter, anteroposteriorly directed sinus into which a number of foramina also open at the level of, or just posterior to, the cribriform plate of the ethmoid. These foramina vary in number, form and position. There is a slight groove in the mesopterygoid roof.

The zygoma has a very tall projection that occupies approximately half its length. The ventral margin of the zygomatic arch is only slightly arched and lies dorsal to the toothrow. Posteriorly, the dorsal margin rises nearly vertically to form the projection which rises to the level of the dorsal edge of the? lacrimal foramen. Its maximum height occurs dorsal to the glenoid surface. Its apex is rounded, converging slightly towards the skull, and its posterior margin convex and vertical to backward-sloping. A masseteric scar occurs on the anterolateral ventral surface of the arch. The zygomatic arches diverge posteriorly at first then flatten to become less divergent posteriorly.

The braincase is oval in shape in dorsal view. It is widest at the level of the post-tympanic processes, narrowest in the interorbital area, and highest dorsal and posterior to the postglenoid processes. There is little development of the lambdoidal crest but in some specimens (QMF31572) it is slightly better developed than in others (QMF31571). A low sagittal crest extends from the supraorbital ridges to the parietal region. Approximately two-thirds along the length of the braincase, within the parietals, is the posterior transverse sinus, along which several small orifices open extracranially.