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CORYSTOID CRABS OF THE GENERA TELMESSUS AND 
ERIMACRUS. 
BY 
James E. BENEDICT, 
Assistant Curator of the Department of Marine Invertebrates. 
(With Plates xxv—xxXVII.) 
This article is based on specimens from Mr. William H. Dall’s Alas- 
kan collection obtained from 1871 to 1874, and on the recent large 
collections made by the U. 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: 
@aOarapace broader, than long 2c. 2 fee eye ncietee A tas ie noe Soci tepals Telmessus. 
iepmateral teethatwiancilam os. 922 sees ee seas s eee alee i oe cheiragonus. 
Pe Aberale bee um SMUT ORM seer syne oes rrr s stapes Nate Sates Saree acutidens. 
fee @acapace longer than broad... 2225-2222 .2- 222. l 22a: scent sees Erimacrus isenbeckii. 
Telmessus White. 
Cancer Tilesius, Mém. de Acad. de St. Pétersbourg, Vol. v, p. 347, 1815. 
Telmessus White, Ann. & Mag. of Nat. Hist., Vol. xviz, p. 497, 1846. 
Platycorystes Brandt, Bulletin Physico-Mathématique de Académie de St. Péters- 
bourg, Vol. vit, p. 179, 1848; also Middendorff’s Sibirische Reise, Band 11, Theil 
I, p. 85, 1851. 
Cheiragonus Brandt, Middendorff’s Sibirische Reise, Band 11, Theil 1, p. 147, 1851. 
~ 
Telmessus Dana, U. 8. Exploring Expedition, Crustacea, Vol. 1, p. 308, 1852. 
Carapace broader than long, pentagonal. Front divided into three 
lobes; median lobe cut into four teeth or denticles; lateral lobes form- 
ing the inner angles of the eyes. Epistome with triangular point ex- 
tending upwards on the median line between the antennule. Basal 
article of the antenna wide, short, flattened; a wing-like projection 
fills the hiatus of the eye. Sternum ofthe 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, 7. 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. 
993 
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