Middle Ordovician – Late Ordovician
Amphilichas is an extinct genus of fast-moving low-level epifaunal carnivores.
Identification in Hand Sample:
- Exoskeleton up to 4cm in length.
- Subtriangular cephalon.
- Pleural areas are approximately as wide as the axis.
- Convex glabella with the elongated lobes.
- Moderately large and holochroal eyes.
- Genal spines moderately short.
- 11 segments in thorax.
- Description. Cranidium approximately as long as wide, moderately convex (sag., tr.), strongly down-flexed forwards. Preoccipital glabella longer than wide, divided by a pair of longitudinal furrows into median lobe and a pair of lateral lobes. Longitudinal furrows deep and narrow, running forwards and slightly inwards from SO to 1/4 length of preoccipital glabella from back, then strongly diverging forwards in a smooth curve to anterior border furrow. Median lobe narrowest at about 1/4 length from back, where it is 55% as wide as basal glabellar width and 17% of anterior glabellar width. Lateral lobe kidney-shaped in outline, wider than base of median lobe, extending forwards to 73% of length of preoccipital glabella. SO deep, transverse medially, curving backwards behind lateral lobes. LO convex (tr.), 13% of cranidial length (sag.), narrowing laterally. Axial furrows narrow and deep, weakly diverging forwards. Anterior border short and gently convex laterally, gradually narrowing inwards. Anterior border furrow deeper abaxially than adaxially. Fixigena poorly preserved, palpebral area convex. External surface closely covered with different sized tubercles and granules.
Fossils of Ohio (1996):
- Amphilichas Raymond has an exoskeleton up to 4 cm in length. The cephalon is subtraingular in outline; pleural areas are approximately as wide as the axis. The glabella is convex and composed of three elongate lobes. Eyes are moderately large and holochroal. Facial sutures are opsithoparian; librigenae are narrow; genal spines are moderately short. The thorax has 11 segments; pleural areas are wider than the axis; each pleura is curved, has a backwards deflection near the middle, and terminates in a spine. The pygidium is large and subtriangular in outline and has three pairs of broad marginal spines. The axis has about three axial rings and a long, pointed terminal piece. Pleural fields have three pairs of pleural furrows and generally two distinct interpleural furrows.
Thomas & Holloway (1988):
- Tetralichine with complete axial furrow in cranidium. Longitudinal furrow commonly complete and adaxially defining parallel-sided lateral lobe, but may be effaced posteriorly. Pygidium with three pairs of spinose pleurae; furrows defining postaxial band meeting at posterior margin or only a very short distance in front of it. Pygidial axis typically with only one complete ring furrow, up to five such furrows occur exceptionally.
Treatise on Invertebrate Paleontology, Part O (1959):
- Longitudinal furrows short (in type species) but mostly reaching occipital furrow. Pygidium usually with pointed axis reaching posterior margin, and unfurrowed 3rd pleurae with single free points.
- Cranadium with tricomposite complete lobes. Occipital lobes absent. Axial furrows complete, or incomplete behind. Pygidium composed of three pairs of pleurae, each with pleural furrow, the first and second pairs complete and projecting freely beyond margin; the third pair incomplete, but with two short, unequal marginal points, the posterior ones very close together; postaxial piece wide, not marked off posteriorly from pleurae. Axis short, undefined behind.
- For the American species at present referred to the European genus Amphilichas, the generic term Acrolichas is proposed, on account of differences in the structure of the pygidia belonging to the American species. The pygidia have three pairs of ribs, all with free tips, but only the first two pairs of ribs bear median grooves; moreover, the axial lobe narrows posteriorly to an acute point which reaches the notch between the free tips of the posterior pair of ribs. Lichas cucullus Meek and Worthen is chosen as the genotype. In the Waynesville member of the Richmond formation, in Ohio, Acrolichas is represented by Lichas harrisi Miller, and a species with coarser pustules is present in the upper part of the Liberty member and the lower part of the Whitewater member of the Richmond.
- Cephalon broadly subtriangular, tuberculate. Anterior lobe of the glabella dominating the other lobes, and continuous with the axis; a single pair of lateral glabella furrows opening directly into the occipital furrow; no third lobes; all lobes depressed convex, all furrows narrow; dorsal furrows concave inward; occipital ring forming a band. Pygidium with two rings on the axis; post-axial piece not defined posteriorly; three pairs of pleurae, each with pleural furrow and free point; third pair incompletely defined from post-axial piece, points short and blunt.