. Bulletins of American paleontology. . 316 Bulletin 238 O (TD O (H) ^ OD CD O 06 88 Text-figure 8.—Transverse serial sections of Rhymhopora sansahensis, n. sp. X 2, USNM 154695 from USNM locality 9045, measurements (mm) from ventral beak. Internally the hinge plate is concave posteriorly and flattened or concave anteriorly with simple elongate cardinal process. Coviparisons. — R. sansahensis, n. sp. is most similar to Rhyn- chopora persinuta (Winchell), 1865, from the Kinderhook of Iowa, and the Byer Member of the Logan Formation of Ohio, and R. cooperensis
. Bulletins of American paleontology. . 316 Bulletin 238 O (TD O (H) ^ OD CD O 06 88 Text-figure 8.—Transverse serial sections of Rhymhopora sansahensis, n. sp. X 2, USNM 154695 from USNM locality 9045, measurements (mm) from ventral beak. Internally the hinge plate is concave posteriorly and flattened or concave anteriorly with simple elongate cardinal process. Coviparisons. — R. sansahensis, n. sp. is most similar to Rhyn- chopora persinuta (Winchell), 1865, from the Kinderhook of Iowa, and the Byer Member of the Logan Formation of Ohio, and R. cooperensis (Shumard), 1855, from the Chouteau Group of Missouri. R. persinuta differs from R. sansahensis in being smaller and in having a narrower more rounded fold and sulcus, with about seven costae in the sulcus, according to Weller (1914, p. 234) [or six or seven according to Hyde (1953, p. 283)], and about seven or eight costae per lateral slope, according to Weller (idem) [or five or six according to Hyde {idein)'\. R. cooperensis differs from R. sansa- hensis in having a narrower fold and sulcus with about six to eight costae in the sulcus and about six or seven per lateral slope; internal- ly the hinge plate is distinctly convex, and a cardinal process is lacking. Remarks. — This species is highly variable in its proportions during ontogeny and in adulthood. Text-figure 9 constructed from data taken from a well-preserved collection from USNM locality 9045, illustrates this variation. Note that there is a distinct tendency in adult specimens for the shells to become relatively more trans- verse. Juveniles remain flat relative to length and width until they attain a length of about five to six millimeters at which time rela-. 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 Paleontological Research Institu
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