Malacologists and philatelists have a common interest in new booklet stamps from the United States and new commemoratives from the Marshall Islands, and if one is both his cup runneth over.

Five 22-cent U.S. stamps feature seashells common to the Atlantic and Pacific coasts of the United States. Five Marshall Islands commemoratives feature uncommon and exotic seashells of the far Pacific.

The $4.40 seashell booklet, intended for over-the-counter sales and containing two panes of 10 stamps at the first-class rate, was just issued in Boston in a ceremony coinciding with 75th anniversary of the Boston Malacological Club, the second-oldest in America devoted to the hobby.

The new booklet has several innovative features. One is a "floating" design, used for the first time on a cover, that creates boundless variety. The seashells on each cover are part of a painting of a strip of 25 varied shells that might be found on a beach. The painting was done by artist-designer Frank Waslick of the Bureau of Engraving and Printing.

Each booklet cover depicts a different position of the painting and shows four or five shells. All the other material on the front and back covers remains constant and was produced subsequent to the printing of the shells.

In addition, the stamps in the booklet are markedly more colorful than the drab Wildlife and Bighorn Sheep in the two preceding booklets. Though printed in three colors, intentional "contamination" of the inks gives the impression of more colors on some of them. That is enhanced by a delicate light blue background.

Each booklet pane has in descending order a pair of these seashells: Frilled Dogwinkle, a univalve shell common to the West Coast from Alaska to California. Univalves include snails, slugs, limpets and whelks.

* Reticulated Helmet, a univalve shell found along the coast from Texas to Brazil.

* New England Neptune, a univalve shell found along the coast from Canada to Massachusetts.

* Calico Scallop, a bivalve shell found from the Carolinas to Texas. Bivalves also include clams, oysters and mussels.

* Lightning Whelk, a univalve shell found in the same area as the Callico Scallop.

The stamps have been produced by intaglio in black and brown, black and purple, and black, brown and purple as basic colors. The top of each pane of stamps in the booklet has a single-digit plate number.

The five multicolored seashell commemoratives of the Marshall Islands, also all 22-cent values, are likewise based on paintings, done by Richard Ellis, one of the foremost painters of marine life. The Marshall Islands in the West Pacific were under Japanese rule until they became a Trust Territory of the United States in the aftermath of World War II. They have become postally independent, issuing their own stamps, on the road to complete self-rule. The atolls literally have hundreds of thousands of species of shells.

The seashells displayed by the Marshalls are the Monodon Murex, intricately sculptured with long fronds; the Black-Spotted Triton; the Diana Conch; the Great Green Turban; and the Rose-Branch Murex, fawn-colored with dark brown ribs and fronds tipped with pink or lavender contrasting with a circular white aperture.

Collectors of first-day-of-issue cancellations of the booklet quintet have a deadline of May 4 -- orders must be postmarked by then -- and alternative ways of ordering.

Collectors acquiring and affixing stamps on envelopes, which must bear addresses, should send the covers to Customer-Affixed Envelopes, Boston, Mass. 02205-9991. A No. 10 envelope is advised for affixing full panes.

Collectors preferring full processing by the USPS should send their covers, with return addresses, to Seashells Stamps, Postmaster, Boston, Mass. 02205-9992. Only full booklet panes removed from booklets will be affixed and canceled; the cost is $2.20 per pane. Personal checks are accepted; cash is not welcome; payment by stamps is rejected.

A 14-cent stamp featuring an iceboat of the 1800s has been added to the ongoing Transportation Series of coil stamps that is a retrospective of early modes of transport.

The stamp has been produced by intaglio in blue in coils of 500 and 3,000. There is one single-digit plate number that appears on every 24th stamp.

First-day cover collectors have an April 22 deadline for orders and alternative ways of ordering.

Collectors affixing stamps on envelopes, which must have addresses, must add 8 cents additional postage to meet the first-class rate. Orders should be sent to Customer-Affixed Envelopes, Postmaster, Rochester, N.Y. 14692-9991.

Those preferring full USPS service should send their addressed envelopes to Iceboat Stamp, Postmaster, Rochester, N.Y. 14692-9992. The Postal Service will add two 4-cent Stagecoach coils to the Iceboat coil so the cost is 22 cents per cover. Personal checks are accepted.