CORYSTOID CRABS OF THE GENERA TELMESSUS AND ERIMACRUS. by-James E. Benedict, Assistant Curator of the Department of Marine Invertebrates. (With Plates xxv-xxvn.) This article is based on specimens from Mr. William H. DalPs Alas-kan collection obtained from 1871 to 1874, and on the recent large collections made by the LI. S. Fish Commission steamer Albatross. The list of localities will show that the Museum is indebted to others for additional specimens. One of the objects of this paper is to call atten-tion to these peculiar crabs, and to invite interest in their habits and life history, of which I believe little is known. The figures were drawn by Mr. A. E. McConnell. The following key sufficiently indicates the species of the two genera: a. Carapace broader than long Telmessus. 1. Lateral teeth triangular cheiragonus, 2. Lateral teeth spiniform acntidens. b. Carapace longer than broad Erimacrus isenbeckii. Telmessus White. Cancer Tilesius, Mem. de l'Acad. de St. Petersbourg, Vol. v, p. 347, 1815. Telmessus White, Ann. & Mag. of Nat. Hist., Vol. xvir, p. 497, 1846. Platycorystes Brandt, Bulletin Physico-Mathematique de 1' Academic de St. Pe"ters-bourg, Vol. vn, p. 179, 1848; also Middendorflf's Sibirische Reise, Band n, Theil . i, p. 85, 1851. Cheiragonus Brandt, Middendortt's Sibirische Reise, Band n, Theil I, p. 147, ISM. Telmessus Dana, U. S. Exploring Expedition, Crustacea, Vol. I, p. 303, 1852. Carapace broader than long, pentagonal. Front divided into three lobes; median lobe cut into four teeth or denticles; lateral lobes form-ing the inuer angles of the eyes. Epistome with triangular point ex-tending upwards on the median line between the antennuhe. Basal article of the antenna wide, short, flattened; a wing-like projection fills the hiatus of the eye. Sternum of the female thickened and sculp-tured around the genital openings. Abdomen of the female deeply con-cave between the genital openings, leaving them fully exposed. Cheli-peds short; ambulatory legs moderately long. This genus contains, as far as known, but two species; one, T.acu-tidens (Stimpson), is common in northern Japan ; another and closely related .species, T. cheiragonus (Tilesius), ranges from Oregon to St. Proceedings National Museum, Vol. XV, No. 900. 223
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