Lower Ordovician (Arenig) – Middle Devonian
Calymenidae is an extinct family of nektobenthic carnivores.
Characteristics of the Family
- Semicircular cephalon with a convex glabella which is bell-shaped or parabolic.
- 2-4 Pairs of lateral furrows on glabella.
- lateral lobes of glabella diminish in size forward.
- Axial furrows bordering glabella are deep.
- Small eye lobes on highest point on genae opposite of glabellar lobes.
- Convex anterior.
- Doublure rolled under borders and not extending inside them.
- Frontal area variable but sometimes extends into frontal spine.
- Connecting sutures converging backward.
- Posterior sections of sutres running backward-outward in anterolaterally convex curve.
Treatise on Invertebrate Paleontology (1959):
- Cephalon semicircular, convex glabella bell-shaped or parabolic, widest across occipital ring or preoccipital lateral may or may not project in front of genae, with 2 to 4 pairs of lateral furrows; lateral lobes of glabella diminishing in size forward, tending to be isolated by shallow furrows from median lobe and independently convex, 2nd (
- ) and 3rd (
- ) lateral lobes (counting forward) may be papillate (that is, with distal edge in contact with projection from gena on opposite side of axial furrow); axial furrows bordering lateral glabellar lobes deep, anterior pit deep; genae highest adjacent to axial furrows, sloping steeply downward anterolaterally; relatively small eye lobes situated on highest part of genae opposite
- glabellar lobes; low eye ridges may be present; convex anterior, lateral, and posterior cephalic borders clearly defined by broad furrows, which become shallow or die out close to facial sutures; doublure rolled under borders and not extending inside them; frontal area variable in length (
- ), in some forms extending into frontal spine; preglabellar furrow and anterior border variable in form; anterior sections of facial sutures running directly forward from eyes and then curving inward to cross-border outside projected line of axial furrows. Rostral suture transverse on doublure in some genera, connective sutures converging backward; rostral plate widest at anterior margin and sharply flexed upward under border; posterior sections of sutures running backward-outward in anterolaterally convex curve to cross border at rounded genal angles which may bear short spine or tubercle on posterior edge inside of suture lines.
- Extended Information:
- ) sutures cut posterior margins just inside relatively long genial spines. Hypostoma longer than wide, subovate middle body divided by short, shallow diagonal middle furrows so that posterior lobe is crescentic; macula faint, smooth; anterior lobe may have raised central portion; exoskeleton at anterior border flexed so that edge faces ventrally, hypostoma with large anterior wing bearing prominent wing process, posterior wing small; wide lateral notch, behind which lateral and posterior borders are wide, with deep median notch adjoining parts of border drawn out into blunt points.
- Thorax with ?11, 12 or 13 segments; axis convex; pleurae bent downward at fulcrum and almost vertical distally; axial rings undivided, but distal portion swollen; deep articulating furrows and apodemal pits, inner part of pleurae horizontal, with deep slightly diagonal pleural furrow, outer part with wide faced partly indented by pleural furrow; articulating processes and sockets in axial furrows and at fulcra; narrow doublure around outer part of pleurae, projecting inward at anterior edges. Pygidium with axis extending almost to posterior margin, sloping steeply backward and sideward; anterior edge of pleural fields curving back, maximum width between anterolateral corners; axis divided by 5 to 8 ring furrows that are deepest abaxially, posterior tip of axis unfurrowed; pleural fields unfurrowed or with deep pleural furrows and shallow interpleural grooves; mostly without border; pygidial doublure narrow and rolled tightly under margins. External surface commonly granulose, tuberculate or both, with deeper parts of furrows smooth. Fine canals penetration exoskeleton scattered over surface, largest on anterior border of Cephalon and posterior part of pygidium, smaller in tubercles along axis.