. Bulletin. Natural history; Natuurlijke historie. ECOLOGY AND EVOLUTION OF THE GASTROCHAENACEA 67. Fig. 6L Natural inlernal casts oitubes oi'Kummelmameucana (Gabb) 1860. Left: regularly shaped tube showing several widely spaced annular constrictions of the tube lining. Each constriction may repre- sent a previous position of the anterior tube wall. Successive anterior tube walls were probably resorbed as the siphons increased in length. USNM 496382, Vincentown Formation, Lower Eocene, New Jersey. Middle and right: two views of an irregularly shaped tube showing the right shell valve. The stra
. Bulletin. Natural history; Natuurlijke historie. ECOLOGY AND EVOLUTION OF THE GASTROCHAENACEA 67. Fig. 6L Natural inlernal casts oitubes oi'Kummelmameucana (Gabb) 1860. Left: regularly shaped tube showing several widely spaced annular constrictions of the tube lining. Each constriction may repre- sent a previous position of the anterior tube wall. Successive anterior tube walls were probably resorbed as the siphons increased in length. USNM 496382, Vincentown Formation, Lower Eocene, New Jersey. Middle and right: two views of an irregularly shaped tube showing the right shell valve. The straight edge on the upper right portion of the right figure probably represents the impression of a posterior tube wall. USNM 496381, Aquia Formation, Paleocene, Maryland. The scale on the left represents 10 millimeters. anterior. This suggests that Kummelia employed considerable anterior- posterior shell movement to accomplish its periodic burrow expansion. This also reinforces the inference that Kummelia tubes did not snow dis- tinctly separated siphonal and shell chambers. The shells of Enfisttdana differ from Kummelia and all other gas- trochaenids in their extreme elongation, sharply truncated anterior, and unusually long and wide pedal gape. The \\^'\c Eufistulana mumia (Spengler) 1783 is strongly compressed dorsoventrally, and it lacks pro- jecting myophores (Fig. 63). The elongate, conical tube of Eufistulana shows well-defined siphonal and shell chambers separated by a double- walled, elliptical diaphragm (Fig. 62). This partition greatly restricts shell movement in the anterior-posterior direction, but does not interfere with rotational activitv within the shell chamber. Burrow elongation in Eufistulana is apparently accomplished by episodic resorption and resecretion of the medial diaphragm and the anterior tube wall. Kiihnelt (1934) suggested thdt Eufistulana increases its. Please note that these images are extracted from scanned page images that may have been
Size: 1721px × 1452px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcollectionbiodiv, booksubjectnaturalhistory
