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188 is entirely undifferentiated. In the latter the tergites of the metasoma are very wide and conical and almost grade into the wide (anteriorly), wedge-shaped or clavate telson. A very important difference lies in the presence of spines in the fourth walking leg of Kokomopterus as compared to the non-spinous character of the same leg in Drepanopterus. The last podomere of the fifth or last walking leg in all species of Drepanopterus terminates in a falcate, and presumably flattened, slightly expanded spine as against the narrow conical shape of the corresponding leg in Kokomopterus. The metastomas, of course, are entirely different.

One species is recognized for the genus:

Part of the generic description and the basis for family separation are derived from new data. A specimen from the Silurian Kokomo dolomite, at Yeoman Quarry, Kokomo, Indiana, which was collected by W. P. Leutze in 1959 and kindly presented to me (No. 74 temporarily in my collection), reveals many details of considerable taxonomic

importance. The overall length of the specimen is estimated at 11 cm. The most interesting feature is the shape of the metastoma, which is roughly oval, with a narrow notch at the anterior and a broad base which is slightly cordate or emarginate (see fig. 98). It measures 8.1 mm. in length and 7.2 mm. in greatest width (see fig. 95). The female, or Type B (see fig. 97), operculum is well preserved, showing even such details as the setae. The appendage is small, about one-third the length of the operculum, and consists of an