Sous-embranchement (subphylum) des Rhynchonelliformea
Classe des Rhynchonellata
Ordre des Terebratulida
Sous-Ordre des Terebratellidina
Super-famille des Terebratelloidea


Genus Pirothyris Thomson, 1927, p. 280

[Type species= Magasella vercoi Blochmann, 1910 (p. 91)]

Small, smooth, elongate oval, strongly biconvex, rectimarginate to slightly parasulcate, beak suberect, symphytium present. Cardinalia thickened, inner socket ridges massive; cardinal process with ovate myophore and prominent anterior boss occupying about half of hinge trough, crura short; loop haptoid.


Diagnosis from volume 5 of the Treatise on Invertebrate Paleontology (2006)

Extant Species of Pirothyris
  • P. vercoi (Blochmann, 1910)
  • Diagnosis

    Pirothyris vercoi  Blochmann, 1910

    Type locality: Backstairs Passage, near Adelaide, South Australia
    Depth range: 29 - 366 m

    Magasella vercoi Blochmann, 1910
    Megerlia willemoesi Tate, 1886 (not of Davidson)
    Pirothyris vercoi: Thomson, 1927

    Diagnosis (Blochmann, 1910)

    Shell small, in outline of a slender pear shape, higher than wide, remarkably thickwalled, light to dark dull coral-red, with a conspicuous finger-shaped hinge process. The greatest width is somewhat in front of the centre. Beak stout, rather strongly bent dorsalwards, and then obliquely truncate, with a moderately large hole. Its sides are rounded, and towards the deltidial plate are finished off in a sharp edge. Deltidial plates large, joining together widely. Lateral edge of the ventral valve in the neighbourhood of the teeth raised dorsally in a low point, further forwards curving ventrally. Front edge distinctly convex dorsally.
    Both valves are nearly equally deep. The accremental striæ are in both quite distinct. To the square millimetre there are about 216 pores, the inner diameter of which amounts to 20 µ. Their outer opening is oval, and measures 25-30 µ by 35-40µ. Both valves are in their hinder part very massive. The thickness of the ventral valve at the beak amounts to about 0'6 mm. This circumstance, together with the somewhat thickened and in many examples distinctly contracted edge, shows with certainty that it has reached a full-grown stage. The colour is a dull lighter or darker coral-red.
    The dorsal valve bears conspicuous tooth sockets, the free wall of which posteriorly projects over the hinge in a triangle. In front of the hinge lies a blunt finger-like hinge process. Under this, looking from the inner side, i.e., also dorsal, appears a hinge-plate, depressed in a furrow-like man- ner in the middle. The hollow space generally existing between the hinge-plate and the wall of the valve is filled up. To the hinge-plate is joined on a stout median septum, reaching as far as the middle or even somewhat further forwards. Its free edge is strongly curved from before backwards, corresponding to the curve of the valve. The brachial apparatus begins with short crura, which bear wide triangular inconspicuous crural processes. The descending limbs reach the median septum widening towards the front, and descending ventrally unite widely with this, run a short distance backwards towards the hinge, and are then united by a bridge somewhat variable in width and position. The brachial apparatus is colourless, or very pale-red. The anterior portion of this is in its general form somewhat variable.