Description of two new species of Ophiuroidea collected during the Snellius Expedition

INTRODUCTION Mr. Austin Hobart Clark, a personal friend of Dr. H. Boschma and during many years curator of the collections of Echinoderms in the U.S. National Museum (Smithsonian Institution), died on October 28, 1954, before his study of the collection of Ophiuroidea from the Snellius Expedition could be completed. A large part of this collection, identified by Mr. Clark, is now preserved in the Rijksmuseum van Natuurlijke Historie, Leiden; a minor portion of the Ophiurid collection still awaits its revisor. Amongst the identified material there are two new species, the descriptions and drawings of which were finished by Mr. Clark before his decease. These were found amongst papers of the late Mr. Clark in the U.S. National Museum by Dr. Fenner A. Chace, Jr. and kindly placed at our disposal for publication in Dr. Boschma's jubilee volume. Both species are based on single specimens (holotypes), now preserved in the collections of the Rijksmuseum van Natuurlijke Historie, Leiden. Ophiarachna snelliusi sp. nov. (fig. 1) Description. — The disk is pentagonal, 11 mm in diameter, and the arms, which are separated at their bases by about twice their width, are slowly and evenly tapering, and 55 mm long. The disk is densely covered with small granules which continue on the oral side as far as the oral shields and run out over the arm bases as far as the seventh side arm plate. The radial shields are very small, oval, half again as long as broad, situated on the edge of the disk on each side of the extension of the granules over the arm bases. The oral shields are about as long as broad, triangular, with the inne