Remarks.—The differences between Ctenopterus and Laurieipterus have been described above in discussion of the latter genus. In comparison with Hallipterus and Mazonipterus the differences lie in the position and characteristics of the eyes and the altogether different ornamentation.
Only one species is recognized for the genus Ctenopterus:
| Ctenopterus cestrotus (Clarke), 1907 | Silurian | New York |
Genus Hallipterus Kjellesvig-Waering, 1963
Diagnosis.—Laurieipteridae of large size; carapace subelliptical, longer than wide, truncated at the base and surrounded by a prominent but unornamented marginal rim; lateral eyes very small, arcuate, close-set and centrally located on the carapace and separated by a prominent median ridge with large ocelli located at the posterior extremity; conspicuous orbital ridges surround the lateral eyes anteriorly and laterally; the ornamentation comprises coarse elongate and confluent pustules arranged in concentric lines particularly prominent on the anterior of the carapace; chelicera simple, elongated; first walking leg with flat movable spines; rest of appendages and opisthosoma unknown.
Type species.—Stylonurus excelsior Hall, 1883.
Distribution.—New York and Pennsylvania.
Stratigraphic range.—Upper Devonian.
Remarks.—This genus of gigantic eurypterids is composed of two famous species, Hallipterus excelsior (Hall) of New York and H. lacoanus (Claypole) of Pennsylvania, and is well known through the famous restorations of Beecher, and later of Clarke and Ruedemann. Unfortunately, these well known restorations, except for the carapace and first legs, were based mainly on the opisthosoma and appendages of other Stylonuracea. Differences between this genus and Laurieipterus or Ctenopterus have been discussed under the Remarks on those genera.
Genus Mazonipterus Kjellesvig-Waering, 1963
Diagnosis.—Stylonuridae of medium size; carapace very elongated, with lateral eyes arcuate and placed anteriorly on the carapace; greatest width of carapace occurs midway; palpebral lobe attached to carapace by a narrow bridge on outer-posterior part of lobe;
