. Brachiopod genera of the suborders Orthoidea and Pentameroidea. Orthoidea; Pentameroidea; Paleontology -- Paleozoic. MORPHOLOGY OF THE ORTHOID SHELL 33 In the Orthidas and Clitambonitidas the two main trunks are clearly visible but instead of being widely divergent as in the Billingsellidas they extend forward near the mid-line of the shell, being separated by a narrow septum only (t. figs. 3, 4; pi. 2, fig. 18; pi. 6, figs. 18, 26; pi. 8, fig. 10). At the front they may or may not diverge. In the higher families of the Orthoidea such as the Dinorthidse and Plectorthida: the pallial markings
. Brachiopod genera of the suborders Orthoidea and Pentameroidea. Orthoidea; Pentameroidea; Paleontology -- Paleozoic. MORPHOLOGY OF THE ORTHOID SHELL 33 In the Orthidas and Clitambonitidas the two main trunks are clearly visible but instead of being widely divergent as in the Billingsellidas they extend forward near the mid-line of the shell, being separated by a narrow septum only (t. figs. 3, 4; pi. 2, fig. 18; pi. 6, figs. 18, 26; pi. 8, fig. 10). At the front they may or may not diverge. In the higher families of the Orthoidea such as the Dinorthidse and Plectorthida: the pallial markings are more complicated but of the same fundamental pattern. In Plcesiomys (see t. fig. 5; pi. 10, fig. 26) the main trunks are short and rather narrow, diverging from the antero-lateral extremities of the diductor scars. The main trunks branch almost immediately after their inception, sending one trunk posteriorly and another antero-medially. Each of these subsidiary trunks gives rise to minor branches toward the front and sides of the shell. In Mhnella (see t. fig. 6; pi. 12, fig. 20) the general arrangement of the trunks is on the plan of D'morthis, but details of the branching are different. Orthostrophia (t. fig. 7) has the two diverg- ent trunks of the Dinorthidx which branch into subsidiary trunks, but in addition has one or two minor trunks extending forward from the adductor tracks. These may actually be branches from the main trunks in front of the diductor impressions, but no lines of contact were observed. In the Dalmanellidaj the two main trunks are visible in many of the genera, extending forward from the diductor impressions. The branching of the main trunks into subsidiary rami is more or less complicated (t. fig. 8; pi. 17, fig. 22).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Schuchert,
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