Oval trigonal; umbos prominent, inflated, slightly opisthogyre, incurved; teeth about 13 anterior, six posterior; resilifer rather small, directed forwards and inwards; dorsal margin straight posteriorly, slightly convex anteriorly, where it is about twice as long as the posterior portion, ventral margin a regular curve; shell smooth, but for obsolete concentric striae and scanty microscopic radial striae; inner ventral margin minutely crenulate.

DIAGNOSIS: A Nucula of middling size, triangularly ovate in outline, with an almost straight posterior margin. Outer shell surface either smooth or with weakly developed, keeled concentric ribs which occasionally are notched by the radial shell structure. Of the known species Nucula pusilla Angas comes closest, but N. beachportensis is larger, less ventricose, with a very short posterior part, a relatively longer and almost straight posterior margin and, in adult specimens, a chondrophore that projects less beyond the hinge plate and that is more forwardly directed. N. beachportensis very probably lives at greater depth, and pusilla in rather shallow water.
DESCRIPTION: valve fairly solid, rather shallow, triangularly ovate in outline, posterior part somewhat depressed. Dorsal margin weakly curved, almost linear near the beak, passing into posterior margin either with a distinct angle or gradually. Posterior margin almost straight, descending vertically from the posterodorsal angulation, or when there is no such angulation, slanting backwards directly from beneath the umbo, or intermediate. Dorsal margin anteriorly shading off into anterior margin, which is nearly straight. Posteroventral angle not sharp, but yet distinct, ventral margin broadly rounded — though straighter posteriorly — and gradually extending into anterior margin. Exteriorly, embryonic shell with microscopic pits, interdissoconch smooth, dissoconch either smooth with some more or less pronounced growth lines on anterior, posterior and ventral areas, or with additional sculpture of weak, irregular, keeled concentric riblets. Radial shell structure distinct on median area, most conspicuous in concentrically ribbed specimens in which shell surface and even ribs may show faint radial lines. Shell colour whitish, sometimes with yellowish concentric zones (possibly an artefact). Periostracum light olive green. Hinge parts not very heavy, with up to about 15 anterior and 9 posterior V-shaped secondary teeth. Anterior teeth row extending over chondrophore, not reaching posterior teeth row. Chondrophore not very salient, oblique, strongly forwardly directed. Adductor muscle scars and pallial line often indistinct. Ventral margin minutely crenulated by radial structure.

MEASUREMENTS: The holotype has an embryonic shell length of about 0.22 mm, an interdissoconch length of about 0.75 mm, a valve length of 5.74 mm, a valve height of 4.97 mm and a valve section of 1.44 mm. (The measurements given by Verco (1907) and copied by Cotton and Godfrey (1938), i.e. length 4.9 mm and umbo-ventral distance 4.6 mm do not apply to the only specimen indicated as "Type" by Verco). The largest valve examined has a length of 6.16 mm.

Off the coasts of southern New South Wales, Victoria, Tasmania, South Australia and Western Australia (fig. 70).