Page:A Revision of the Families and Genera of the Stylonuracea (Eurypterida).djvu/27

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191
KJELLESVIG-WAERING: STYLONURACEA

line clearly separating the anterior rostral area from the inclined rear of the shield; opisthosoma is unknown except as fragments.

Type species.—Stylonurus elegans Laurie, 1899.

Derivation of generic name.—Named in honor of Malcolm Laurie for his many original contributions to our knowledge of Eurypterida and Scorpionida.

Distribution.—Scotland.

Stratigraphic range.—Silurian, Gala-Tarannon.

Remarks.—Laurieipterus differs greatly from the other genera of the Laurieipteridae, and comparison is needed only with Ctenopterus, the genus under which this strange eurypterid had been included since the Clarke and Ruedemann monograph of 1912. Firstly, the carapaces are very different; that of Laurieipterus is highly bulbous at midsection with an extremely narrow base, as against the anteriorly converging carapace of Ctenopterus with its wide base and unusual cheek pouches. The latter has a greatly different arrangement of the spines of the anterior legs, and has one podomere more on the last two legs. There are numerous other differences not necessary to detail here (see Clarke and Ruedemann, 1912, p. 286; Laurie, 1899, p. 580, and Waterston, 1962, p. 143).


Genus Ctenopterus Clarke and Ruedemann, 1912

Diagnosis.—Laurieipteridae of small size; carapace elongated oval, longer than wide, and with widest part in posterior fourth, narrowing anteriorly to less than half the width, anterior margin prominent and ornamented with fringe of spines; lateral eyes elongated arcuate, with median ocelli approximately midway between; two oval cheek-like ridges are on each side of the carapace; first and second appendages unknown, third and fourth very long and armed with slender, paired spines of even length, the last two walking legs extremely long, the sixth reaching to the twelfth tergite, these two legs terete and bare of spines, all legs terminating in a pointed, conical joint; podomere-count: ?–?–8–8–9–9; metastoma unknown; preabdomen slender, but well differentiated from the postabdomen; opercula not well known; telson presumably a long spike; ornamentation highly variable, consisting of pustules and scales.

Type species.—Stylonurus cestrotus Clarke, 1907.

Distribution.—New York.

Stratigraphic range.—Silurian.