In his original description of the worm Lamellibrachia barhami, found in a depth of 1125 m in the northeastern Pacific, Webb (1969: 31) mentioned "as yet unidentified copepods which live in quite large numbers in interlamellar pockets in the tentacular crown". Webb regarded the worm host as a pogonophoran (Order Vestimentifera), but Dr. J. van der Land of the Rijksmuseum van Natuurlijke Historie, Leiden, believes that the genus Lamellibrachia should be referred to the Annelida, Vestimentifera (in a letter to the author, 13 December 1971). Copepods are not known to be associated with Pogonophora, but many live on polychaete annelids. Through the kindness of Dr. W. Vervoort, Rijksmuseum van Natuurlijke Historie, Leiden, I have had the opportunity to study a small number of cyclopoid copepods found with an annelid worm (Vestimentifera) taken off Guyana during the Guyana Shelf Expedition "CICAR 15" (Cooperative Investigation of the Caribbean and Adjacent Regions, Cruise No. 15). The host is a second and new species of the genus Lamellibrachia, according to Dr. van der Land who is currently studying it. Unidentified copepods were seen in serial sections of the tentacles of this host specimen. The study of the copepods has been aided by a grant (GB-8381X) from the National Science Foundation of the United States. I am indebted to Dr. Jan H. Stock, Zoölogisch Museum, Amsterdam, for examining the drawings and offering valuable suggestions. CLAUSIDIIDAE Embleton, 1901 Tychidion n. gen. Diagnosis. — Male: Body cyclopoid. Urosome 5-segmented, though the apparent genital segment may represent a fusion of the genital segment and