17 99 Buchania n.sp. (helderbergiae) Shaly limestone @ Lower Helderberg group Clarksville, N.Y. 100 Strophostylus elegans, Hall. Shaly limestone @ Lower Helderberg group Clarksville, N.Y. 101 Murchisonia ? sp. (casts) Shaly limestone (2 Lower Helderberg group Indian Ludden, Albany Co., N.Y. 102 Murchisonia sp. (cast) Shaly limestone Lower Helderberg group Indian Ludden, N.Y. 103 interiors of Murchisonia fibrata Hall. Shaly limestone @ Lower Helderberg group Clarksville, N.Y. 104 Murchisona fibrata, Hall Shaly limestone (3 Lower Helderberg group Clarksville, N.Y. 105 Loxonema attenuatum, Hall. Shaly limestone Lower Helderberg group Clarksville, N.Y. 106 Platyceras n. sp. (Compositum Becker) Shaly limestone Lower Helderberg group Clarksville, N.Y. 107 Platyceras n. sp. Upper Pentamerus limestone Lower Helderberg group Clarksville, N.Y. 108 Platyceras n.sp. Shaly limestone Lower Helderberg group Clarksville, N.Y. 109 Platyceras n.sp. (involutum Becker) Shaly limestone (5 Lower Helderberg group Clarksville, N.Y. 110 Platyceras perlatum, Hall. Shaly limestone Lower Helderberg group Clarksville, N.Y. 111 young individuals of Platyceras Shaly limestone (7 Lower Helderberg group Clarksville, N.Y. 112 Platyceras tenuiliratum, Hall Shaly limestone (4 Lower Helderberg group Clarksville, N.Y.