. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 154 Bulletin Museum of Comparative Zoology, Vol. 138, No. 4. Plate 21. Diagrammatic illustration of the anatomy of Heterodonax ludwigii (Krauss): 1, anterior adductor muscle; 2, labial palp; 3, inner demibranch; 4, outer demibranch; 5, posterior adductor muscle; 6, excurrenf siphon; 7, incurrent siphon; 8, cruciform muscle; 9, siphonal retractor muscles; 10, foot. species agree in detail with the diagnosis of the genus Heterodonax Morch 1853 (type-species, by monotypy, Tellina hi- maculata Linnaeus 1758) as given by D
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 154 Bulletin Museum of Comparative Zoology, Vol. 138, No. 4. Plate 21. Diagrammatic illustration of the anatomy of Heterodonax ludwigii (Krauss): 1, anterior adductor muscle; 2, labial palp; 3, inner demibranch; 4, outer demibranch; 5, posterior adductor muscle; 6, excurrenf siphon; 7, incurrent siphon; 8, cruciform muscle; 9, siphonal retractor muscles; 10, foot. species agree in detail with the diagnosis of the genus Heterodonax Morch 1853 (type-species, by monotypy, Tellina hi- maculata Linnaeus 1758) as given by Dall (1900: 973), Thicle (1935: 908) and Olsson (1961: 354). The genus Heterodonax belongs to the family Psaminobiidae. Anatomically, it is characterized by plicate gills and small palps. The ligament is set upon a raised nymph, and the hinge plate is broad. There are really no lateral teeth present, and an escutcheon is not developed. The general features of the Psammobiidae, namely the nature of the gills and palps, are illustrated in Gari teUinelki (Yonge 1949: 37, fig. 6). Further, the puq)le shell coloration, with its tendency to ra\' formation, is often en- countered in the Psammobiidae and par- ticularly in Heterodonax. For these reasons the species named TcIIina lud\. by Krauss is here removed from Tellina and placed in Heterodonax. Heterodonax lnduiii,ii exhibits a con- siderable amount of variation, especially in regard to shape and coloration. Further, the outline of the valves changes during ontogeny. In smaller, immature specimens there is a tendency to be proportionately more elongate or rather subelliptical in out- line, whereas in adults the shell is some- what more rounded to subrectangular. Some individuals may have a tendency to pointedness posteriorly, and frequently the. 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 pe
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