SYNOPSIS OF THE LUCTNACEA AND OF THE AMERICAN SPECIES. By William Healey Dall, Honorary Curator, Dirmon of Bfollusls. The present paper is a continuation of the series of synopses of various groups of our marine Invalve shells, of which the Leptonaeea, Solenida?, Tellinidai, and Cardiidw have already appeared in these Proceeding's, ^ and other groups have been similarly treated elsewhere. The Lucinacea is a fairly homogeneous group of families, apparently of very ancient lineage if the Silurian type referred to it is really akin. Mesozoic forms certainly occur, and, in the Tertiary, they are more numerous, more varied, and of greater size than in the recent fauna. These papers make no attempt to review subordinate groups oldei-than the Tertiary which are not represented in the Tertiary or recent faunas. The older groups require more time and material than is at the w^riter's disposal to treat them with thoroughness. On the other hand, most of the Tertiary genera are represented in the recent fauna, and some light on their affinities in doubtful cases can be gained from existing types. The systematic arrangement of the Lucinacea, especially that of the typical family, is exceptionally confused, as it is more than half a century since the group, as such, has been revised even among the recent species, and makers of manuals seem to have accepted current statements with more than usual good nature. Many of the most common species go by names to which a very superficial examination would show they have no sufficient claim, and the manner in which unlike things have been lumped together is quite sur])rising, ' Synopsis of the Recent and Tertiary Leptonaeea of North America and the West Indies. Proc. U. S. Nat. Mus. XXI, pp. 873-897, with plates lxxxvii, lxxxviii (No. 1177) , June, 1899. Synopsis of the Solenidpe of North America and the Antilles. Proc. U. S. Nat. Mus. XXII, pp 107-112 (No. 1185), October, 1899. Synopsis of the Family Tellinidte and of the North American species. Proc. U. S. Nat. Mus. XXIII, pp. 285-326, with plates ii-iv (No. 1210), November, 1900. Synopsis of the Family Cardiidae and of the North American species. Proc. U. S. Nat. Mus. XXIII, pp. 381-392 (No. 1214), December, 1900. Proceedings U. S. National Museum, Vol. XXIII— No. 1237. 779
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