Synonyms: Pseudomonaspis Richter and Richter, (1917)
Middle Ordovician – Middle Devonian
Acidaspis is an extinct genus of fast moving, low level epifaunal carnivores.
Identification in Hand Sample:
- Small, spiny, and covered with numerous tubercules.
- Glabella convex, overhangs the cephalon.
- Cephalon short and wide.
- Thick, long medial spine on occipital ring.
- Thorax has 10 segments.
- Pygidium small, with seven pairs of marginal spines.
- Complete specimens are exceedingly rare.
- Body small, with a general sub-ovate or sub-elliptic outline rather distinctly convex. Cephalic shield sub-semicircular, and rather more convex than the body, apparently rounded in front, with the lateral angles produced into slender, mucronate, somewhat curved spines that extend obliquely outward and backward to points opposite the fifth or sixth thoracic segment. Glabella, including the neck segment, one third longer than wide with an oblong, sub-elliptic outline, the widest part being slightly behind the middle and between the eyes, lateral lobes two, on each side of slightly oval outlines, with their longer diameters directed a little obliquely outward and forward; the posterior one being slightly larger than the anterior, while both are separated by well-defined furrows from the central, rather narrow part of the glabella, as they are separated from each other, or from the cheeks on each side; anterior lobe about as large as all four of the lateral lobes, twice as wide as the narrowed central part of the glabella behind it, and apparently rounded in front; between the lateral lobes and each eye a kind of outer or supplementary lobe, or protuberance, as large as each two of the lateral lobes, occurs; while from the outer side of each of these protrudes the small prominent palpebral lobe, which arrangement places the small eyes quite remote from each other; eyes unknown, but apparently small, prominent, and directed laterally; movable cheeks not well preserved in the specimen studied, but apparently narrow, and sloping abruptly from the eyes laterally; neck segment comparatively large, prominent, with a central tubercle, and well defined by the neck furrow, which arches forward in the middle.
- Thorax nearly twice as long as the cephalic shield, and about one-fourth wider than long, exclusive of the produced extremities of the pleurae, with its segments strongly arched upward, but not forward. Lateral lobes comparatively rather depressed, and rounding oil gradually toward the lateral margins; pleura terminating in mucronate spines directed outward and more or less backward, the posterior ones being longer, and directed more nearly backward.
- Pygidium small, and with its mesial lobe composed of about three segments; lateral lobes consisting apparently of about three or four segments, each of which terminates in an acute spine, the lateral ones of which are larger than the others, and curved backward.
- Entire surface comparatively rather coarsely granular, the granules being larger on the head than elsewhere; while on each of the pleurae, a larger granule or very minute tubercle occurs, at a point about halfway out to the knee, or geniculation, at which latter point there is also some appearance of another, thus making two rows of these coarse granules along each lateral lobe.
- Entire length, exclusive of the spines of the Pygidium, about 0.25 inch; length of head, 0.08 inch; breadth, exclusive of lateral spines, 0.15 inch; breadth, between eyes, 0.10 inch; length of thorax, about 0.11 inch; breadth of same anteriorly, exclusive of the extended ends of the pleurae, 0.14 inch.
- Although most unwilling to multiply names the very remarkable form of the head or shield of this trilobite the posterior end of its central lobe projecting over the body in the form of a stomacher and rendering it totally distinct from any published figure induces me to propose it as a new genus.