Page:A Revision of the Families and Genera of the Stylonuracea (Eurypterida).djvu/16

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of Stylonurella differs greatly from the subrounded, wider than long, carapace of Parastylonurus.

In the shape of the carapace and position of the eyes, Stylonurella has a resemblance to Kokomopterus, however the altogether different type of prosomal appendages is a difference that precludes the necessity for further comparison.

Recognized species for this genus are:

Stylonurella arnoldi (Ehlers), 1935 Upper Devonian Pennsylvania
Stylonurella modestus (Clarke and Ruedemann), 1912 Ordovician New York
Stylonurella otisius (Clarke), 1907 Silurian New York
Stylonurella ruedemanni (Størmer), 1934 Siluro-Devonian Norway
Stylonurella spinipes (Page), 1859 Silurian Scotland

Genus Parastylonurus, new genus

Diagnosis.—Stylonuridae of small to medium size; prosoma rounded-quadrate; wider than long, with lateral eyes, arcuate and located on anterior half of the carapace; metastoma very long, with deep triangular notch or deeply cordate and with base truncated; first three walking legs very short with single opposable spines on each joint; last two walking legs very long, reaching to the last tergite; podomere-count: ?–?–7?–8–9–9; ornamentation consists of scales; opisthosoma narrow, undifferentiated; telson spike-like.

Type species.—Stylonurus ornatus Laurie, 1892.

Distribution.—Scotland, England, New York and Pennsylvania.

Stratigraphic range.—Ordovician, Silurian and Devonian.

Remarks.—Parastylonurus includes more forms previously included in the genus Stylonurus than do the other genera described here. However, in my opinion, the development of distinct trilobation in the genus Stylonurus sets that genus irrevocably apart from the species that are here referred to Parastylonurus. The position of the eyes is also a major generic difference.

The following species are recognized:

Parastylonurus ? beecheri (Hall), 1884 Devonian Pennsylvania
Parastylonurus macrophthalmus (Laurie), 1895 Silurian Scotland
Parastylonurus ? megalops (Salter), 1859 Siluro-Devonian England
Parastylonurus myops (Clarke), 1907 Silurian New York, Pennsylvania