latus in recognition of the very pronounced development of the alveolar processes surrounding the spines.
The endognathites figured above are in many respects similar to those figured by Clarke and Ruedemann (N. Y. State Museum Memoir 14, 1912, Vol 2, p. 541) under the name Stylonurus (Ctenopterus) multispinosus. This species possesses elongated joints fringed with spines along the posterior margin. While there is a difference in the general shape of the joints the chief distinction between the species multispinosus and alveolatus is in the prominent development of the alveolar process and the unusual size of the distal spine in the specimen from the Bays sandstone. Stylonurus (Ctenopterus) multispinosus Clarke and Ruedemann occurs in the Pittsford shale of the Middle Silurian. It is interesting to find an Ordovician species so strikingly similar to a form which comes from a much higher horizon in the Silurian.
Dr. Bassler and others have correlated the Bays sandstone with the Lorraine of New York. Dr. A. W. Grabau has made it the equivalent of the late Maysville and Richmond. The general character of the fossils collected with the Eurypterid fragments certainly establishes a correlation with the Upper Ordovician, and probably Maysville rather than Richmond.
In the "Table of the Geologic Distribution of the North American Species of Eurypterids at Present Known " (N. Y. State Bull., Memoir 14, 1912, p. 431), representatives in the Ordovician have been reported from the Normanskill shale, the Schenectady beds, and the Utica. One species has been reported from the Richmond.
The bionomic interest of the find lies in the association of the fragments with a typical marine fauna. One of the joints was found resting against a specimen of one of the most abundant of the Bays brachiopods. Such an association falls in line with the general occurrence of Ordovician Eurypterid remains with those of marine organisms. The delta-like and near-shore character of the Bays sediments is evident. But though the fragmental character of the Eurypterid remains indicates transportation and a consequent breaking up of a complete exoskeleton, the occurrence at Lyons Gap gives no indication that this took place in a fresh water stream rather than in surf along the shore. On the whole, the find seems to confirm Laurie's suggestion that Stylonurus possessed purely littoral habits.
Dept. Geology, Harvard University.