Abdomen with twelve segments, the anterior nine of which have a pair of ventral appendages to which the branchiae are attached; the posterior segment has a central spatulate-shaped section that, combined with swimmerets, forms a strong caudal fin.
The description of the branchiae will be found under the description of Sydneyia, the typical genus of the Limulava.
Observations.—The sub-order Limulava differs from the Eurypterida, to which it is most nearly related, in having a large epistoma similar to that of the Trilobita; in not having a metastoma, chelate antennae, and swimming cephalic appendages; and in having a broad fan-shaped caudal fin, and branchial appendages more or less unlike the lamellar branchiae of the Eurypterida and Xiphosura.
Family SIDNEYIDAE, new family
Cephalo-thorax small, without lobes, eyes marginal; ventral side with large epistoma, five pairs of movable appendages, the gnathobases of the three posterior pairs forming organs of manducation. Abdomen twelve-jointed, the three posterior segments annular and narrow, the terminal one forming, with lateral swimmerets, a fan-like tail; nine anterior segments with a pair of ventral branchial appendages on each; the three posterior segments without ventral appendages. Surface smooth or ornamented by narrow, irregular, fine, imbricating ridges.
Genus SIDNEYIA, new genus
Body elongate, broadly oval in outline, attaining as now known a length of 17 cm., covered with a thin dorsal shield or crust, divided into a short cephalon, broad anterior abdomen, and narrow posterior abdominal portion. Cephalo-thorax transverse, short, depressed convex, as compressed in the shale, with broadly rounded frontal margin and antero-lateral angles; margins smooth. Eyes reniform and situated near the postero-lateral outer margin. Ventral side with five pairs of movable appendages. The anterior pair are large, long, simple, jointed antennae; second pair, slender and jointed; third pair with numerous spines on the front side of the joints and with variously developed chelate-like outer joints (see pl. 4) ; fourth pair, slender and jointed; fifth pair with a large basal joint, and an outer, broad joint or palp that is fringed with fine branchial setae or spines. A large epistoma is attached to the front margin and back of it the gnathobases of the appendages, the three[1] posterior pairs of which form the organs of manducation.
- ↑ See description of species, S. inexpectans (p. 25).
