Page:A Revision of the Families and Genera of the Stylonuracea (Eurypterida).djvu/25

, rather broad lanceolate joint, with two triangular joints at the distal end. A transverse suture occurs at the midsection of the opercular flaps. The lanceolate joint, as well as the surrounding parts of the operculum, are very hirsute, being covered with dark brown tactile setae. The fine punctation that occurs on the triangular points likely represents sites where the setae had broken away. The carapace measures 19.4 mm. in length with an estimated width of 26.0 mm. The ventral shield apparently comprises an undivided, or non-sutured, plate of 6 mm. in width at the anterior part. There is no trace of an epistoma, or of sutures, although the preservation of this part does not allow complete confidence. The prosomal appendages of this specimen are too poorly preserved for description. The dorsal side of the specimen, however, retains the original coloration as is common with the eurypterids of the Kokomo assemblage. The specimen is shiny, fairly dark brown; but curiously it reveals a narrow, very dark brown line, over one millimeter wide, that runs through the center of the dorsal length of the opisthosoma. This is not to be mistaken for a suture as it is definitely a color distinction. This is the first instance of a purely colored ornamentational pattern known in the stylonuroids. The dorsal side is covered with scales, most of which are semi-lunar in shape; others become rather pointed. The doublures of the tergites are heavily hirsute.

Diagnosis.—Stylonuracea with ventral shield having median suture, but no epistoma; metastoma pyriform, slightly concave anteriorly, broadly rounded posteriorly.

The family remains monotypic and is known only from the Devonian of Germany and possibly New York.

Diagnosis.—Carapace longer than wide, rounded anteriorly, and with lateral eyes reniform, located slightly in front of midsection; first two (or three) pairs of walking legs with spines, last two pairs without spines; male appendage short, with two distal spurs; podomere-count: ?–7–8–8–9–9.

Type species.—Rhenopterus diensti Størmer, 1951.

Distribution.—Germany and New York (?).