. Bulletins of American paleontology. Silurian Plectograptine Graptolites: Lenz on Silurian and Devonian graptolites of Nevada is also relevant. Elsewhere in the worid, studies of uncompressed and isolated Wenlock and Ludlow retiolitids include: iso- lated specimens of Stoniatograptus Tullberg, 1883 and Gothograptus nassa (Holm, 1890) by Holm (1890), and of Gothograptus nassa by Wiman (1896), both from Gotland; the pioneering studies of Eisenack (1935, 1951) on the Silurian, particularly Ludlow, glacial er- ratics of northern Germany, which yield a number of beautifully preserved taxa; Obut an
. Bulletins of American paleontology. Silurian Plectograptine Graptolites: Lenz on Silurian and Devonian graptolites of Nevada is also relevant. Elsewhere in the worid, studies of uncompressed and isolated Wenlock and Ludlow retiolitids include: iso- lated specimens of Stoniatograptus Tullberg, 1883 and Gothograptus nassa (Holm, 1890) by Holm (1890), and of Gothograptus nassa by Wiman (1896), both from Gotland; the pioneering studies of Eisenack (1935, 1951) on the Silurian, particularly Ludlow, glacial er- ratics of northern Germany, which yield a number of beautifully preserved taxa; Obut and Sobolevskaya's (1965) studies of isolated specimens of Gothograptus eisenacki Obut and Sobolevskaya, 1965; Obut and Zas- lavskaya's (1976) study of isolated material of Retiol- ites Barrande, 1850, Pseudoretiolites Boucek and Miinch, 1944, and Sokolovograptus Obut and Zaslav- skaya, 1976 from boreholes in Siberia; and finally, the important study of Obut and Zaslavskaya (1983, and its English translation [1986]), which discussed Silu- rian retiolitid classification and recognized as new the genus Agastograptus Obut and Zaslavskaya, 1983. TECHNIQUES FOR RECOVERY OF GRAPTOLITES FROM NODULES Because they commonly have a thin siliceous coat- ing, nodules are broken open to aid in the acid-diges- tion process. For best recovery of graptolites, partic- ularly the delicate types, acid dissolution must be very slow, using only 1-2% HCl*, with small amounts of acid being added daily or more often. Periodically, the surface of the acid is skimmed gently with a 60-100 mesh stainless steel sieve to collect graptolites floating on the surface. Most graptolites float because of the CO2 bubbles inside or clinging to the rhabdosomes. The graptolites in the sieve are then rinsed very gently in hot water to wash away clays or other fine particles as well as some of the organic matter derived from the nodules^. The residue is then gently washed in absolute alcohol to remove all traces of the oi
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