Page:A Revision of the Families and Genera of the Stylonuracea (Eurypterida).djvu/18

182 location, preclude the need for any comparison. There are no other stylonuroids with the characteristics of Brachyopterella.

The species that are referred to this genus are:

Diagnosis.—Stylonuridae of small size; carapace longer than wide, suboval, pointed anteriorly, with the base considerably narrower than the greatest width, which is at midsection, base concave; eyes crescentric, large, located slightly in front of the middle of the carapace, axes of eyes slightly convergent anteriorly, palpebral lobes very large and circular, attached by narrow bridge to the carapace at the inner part of the eyes; ocelli midway between the eyes; marginal rim either not present or very narrow; ventral shield mostly unknown but bordered by an unsutured marginal rim; no ornamentation present.

Type species.—Dolichopterus ? testudineus Clarke and Ruedemann, 1912.

Derivation of generic name.—Named in honor of John M. Clarke for his many contributions to our knowledge of the Eurypterida.

Distribution.—Scotland (?), New York.

Stratigraphic range.—Silurian.

Remarks.—Except for the Dolichopteridae, nearly all the Stylonuracea are found in argillaceous or sandy sediments, but Clarkeipterus is one of the few exceptions as it occurred in a calcareous-magnesian mud. Clarkeipterus is extremely rare; it is known from only one specimen, though a very well preserved one, from the famous Bertie waterlime (Fiddlers Green dolomite) of Herkimer County, New York. The genotype has been doubtfully referred to Dolichopterus or Brachyopterus by authors, including myself, but it seems preferable now that the carapace should be relegated to the redefined family Stylonuridae, because of the crescentic eyes. There is little purpose in comparing this genus with any others as it is unique.

The following species are recognized: