Page:A Revision of the Families and Genera of the Stylonuracea (Eurypterida).djvu/12

176 that it is either a dolichopterid or one of the stylonuroids. The ornamentation is more typical of such stylonuroids as Hallipterus. Nevertheless, the flattened podomeres indicate that if Tarsopterella is a stylonuracean, it should probably be referred to the Dolichopteridae. This is done here with considerable misgivings until the ventral side is known or some more prosomal appendages are found of this highly spectacular eurypterid. It is not precluded that Tarsopterella may not belong among the Eurypteracea.

The following species are recognized:

Diagnosis.—Ventral shield and metastoma unknown; eyes located in posterior half of carapace, opisthosoma undifferentiated, trilobation present; last two legs very long.

The above family diagnosis is based on the type species of Stylonurus as restricted here. However, if genera such as Stylonuroides, Stylonurella, Parastylonurus, Brachyopterus and Brachyopterella are used in the diagnosis, then a much better and more complete diagnosis can be made. I suspect, however, that some of these genera will be found eventually to have no significant affinities with the type genus. It is almost certain that further revisions in the diagnosis of the family will be forthcoming with discovery of additional material. With these reservations in mind, the diagnosis of the family may further include:

Diagnosis.—Ventral shield with epistoma; metastoma very narrow, with deep triangular notch or deeply cordate anteriorly, and with base truncated.

It should be noted that when the underside of Stylonurus powriensis Page, the genotype, is known, genera such as Parastylonurus, Stylonuroides, Stylonurella, Brachyopterus, Brachyopterella, and others here included in the Stylonuridae, may well be found to belong to other and distinct families.

The following genera are recognized for this family:

Stylonurus Page, 1856

Stylonurella, new genus

Stylonuroides, new genus

Parastylonurus, new genus