Page:A Revision of the Families and Genera of the Stylonuracea (Eurypterida).djvu/22

186 The following species are recognized for the genus:

Diagnosis.—Stylonuracea with band-like ventral shield of the prosoma, without epistoma; metastoma broadly pyriform, very wide posteriorly and notched anteriorly and with a broad emargination at the posterior end.

Type genus.—Kokomopterus new genus.

The differences between this family and others are significant. It resembles the Rhenopteridae in the band-like ventral shield and lack of epistoma. However, the totally different metastomas are sufficient for separation, and further comparison with that family as well as the other Stylonuracea is considered superfluous. At present the family is monotypic and is known only from the Silurian of Indiana.

In comparison with the Drepanopteridae, the difference lies in the ovate, anteriorly cordate metastoma as against the altogether different-shaped structure described above for the Kokomopteridae. Previously, the type species of Kokomopterus (K. longicaudatus [Clarke and Ruedemann]) had been mistaken for a Drepanopterus.

Diagnosis.—Kokomopteridae of small size; carapace subquadrate, slightly wider than long, lateral margins parallel; eyes arcuate, with axes parallel, and located in the anterior half of the carapace, considerably apart from one another; ventral shield probably consisting of an undivided plate, with narrow marginal rim; prosomal legs stylonuroid, but increasing posteriorly in a gradual manner; podomere-count: ?–?–?–8–9–9; the second to fifth legs armed with single, unequal, opposable spines; last leg without spines and reaching to the eleventh opisthosomal tergite; all legs terminate in single spine; metastoma broadly pyriform, with narrow notch at anterior end and broadly but slightly emarginate at the posterior; opisthosoma differentiated into a preabdomen of seven tergites and a much narrower postabdomen of five, of which the twelfth tergite is long, rectangular