. Annual report. New York State Museum; Science; Science. 72 NEW YORK STATE MUSEUM in Tetragraptus fruticosus [see Mem. 7, text fig. 11, also ibid. pi. 10]. In those groups of Tetragraptus and Didymograptus, in which the recurving of the branches takes place close to the sicula, as in Tetra- graptus si mi lis [ibid, text fig. 58] the sicula and first thecae become spinose. Frequently the difference in aspect between these first, strongly spinose thecae and the later ones is strongly marked [Leptograptus flaccid us var. spinifer]. In several species of Didymograptus (D. subtenuis) and Nemagrapt
. Annual report. New York State Museum; Science; Science. 72 NEW YORK STATE MUSEUM in Tetragraptus fruticosus [see Mem. 7, text fig. 11, also ibid. pi. 10]. In those groups of Tetragraptus and Didymograptus, in which the recurving of the branches takes place close to the sicula, as in Tetra- graptus si mi lis [ibid, text fig. 58] the sicula and first thecae become spinose. Frequently the difference in aspect between these first, strongly spinose thecae and the later ones is strongly marked [Leptograptus flaccid us var. spinifer]. In several species of Didymograptus (D. subtenuis) and Nemagraptus (N . exilis Lapworth, text figure 4) only the sicula and one theca on either side are armed with spines, but these are found exactly where the change in direction of the branches takes. Fig. 4 Nemagraptus exilis var. linearis nov. Shows spines of primary thecae. x 5 Fig, 5 Diplograptus angustif olius Hall. Sicular end showing character of spines, x 7 Fig. 6 Glo sso- graptus quadrimucronatus var. cornutus nov. Sicular end showing lateral spines, x 7 Fig. 7 Cryptograptus tricornis (Carrulhers). Aperture of sicula showing four spines, x 7 place and thereby a part of the branch is projected. Among the Diplo- grapti either the virgella alone grows out needlelike, or it is accompanied by the opposite spine of the sicula and two more powerful spines grow from the first two thecae ; this even in forms where the later thecae are wholly unarmed, as in Diplograptus a n gu s t i f o 1 i u s [see text fig. 5] and D. foliaceus [see text fig. 286]. In some varieties, as in D. folia- ceus var. calcaratus and D . t r i f i d u s Gurley these spurs attain such relatively great size that they become the most striking feature of the colony [see text fig. 295]. InGlossograptus quadrimucronatus the thecal apertures are each protected by a pair of lateral spines, but the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - co
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