302 THE VOYAGE OF H.M.S. CHALLENGER. 



Basals triangular or rhomboidal, not meeting laterally on the exterior of the calyx. 

 The two outer radials united by syzygy. The grouping of the ray-divisions and the 

 number of their component joints are somewhat irregular. Primary arms of two to six 

 (usually three or four) distichal joints ; secondaries of two to eighteen (usually seven to 

 nine) palmar joints ; tertiaries of six to fourteen joints, and occasionally another division 

 after eight or ten joints more. The tertiary arms which divide are often only the two 

 outer ones in each group of four, so that the distichal axillary bears six arms, viz., 

 2, 1 ; 1,2; but there are sometimes " more than a hundred arms." ^ The first two joints 

 beyond each axillary united by syzygy, with a pinnule on the epizygal. No other syzygies 

 on the arms, which consist of about a hundred smooth, oblong joints, the outermost ones 

 overlapping slightly. Distichal and palmar pinnules very large and stout, with thick 

 lower joints, those of the later arm-divisions and of the free arms being much smaller. 

 The joints of these large lower pinnules have the distal edge raised into a strongly marked 

 keel which projects forward over the base of the next joint ; and this feature recurs on 

 all the pinnules of the arms, though it is less distinct in their middle and outer portions. 



The perisome uniting the rays up to the level of the distichal axillaries is paved by 

 large, closely set plates. Similar plates cover the ventral surface of the disk and arm- 

 bases. Arm-groove moderately wide, and protected by numerous irregular plates. 

 Pinnule-ambulacra have covering plates, but no definite side plates. Colour in spirit or 

 dry, a light yellowish-brown. 



Localities. — Various parts of the Caribbean Sea — Nevis, Martinique, Barbados, 

 Guadeloupe (Dr. Schramm) ; off Saba Island, 320 fathoms (Captain Cole). This species 

 was only once dredged by the U. S, Coast Survey steamer "Blake," cruise of 1878-79, 

 No. 157, ofi" Montserrat, 120 fathoms. 



Remarks. — The specific name caput- Medusce, which was originally bestowed by 

 Lamarck on the West Indian Pentacrinus described by Guettard, was used by Miller, 

 Goldfuss, Mtiller, and all later writers till the year 1864. In August of this year the 

 late Sir WyviUe Thomson* published a popular article on Sea Lilies, in which he' ex- 

 pressed the opinion that the fossil Pentacrinus hriareus, a widely different species from the 

 recent Pentacrimis caput-Medusce, " seems, however, to have a just claim to be recognised 

 as the type of the genus Pentacrinus ; " and he therefore proposed to give the generic 

 name Cenocrimis to the West Indian species, for which he retained the original title 

 Caput-Medusce. Lixtken," however, reverted to the original specific designation employed 

 by Linnaeus,'* and called the type Pentacrinus asteria. In the following year*^ Thomson 

 referred to it as Pentacrinus {Neocrinus) asterias, Linn. ; but he subsequently" gave up 



1 See "Wyville Thomson, The Intellectual Observer, August 1864, p. 5. 



2 The Intellectual Observer, August 1864, p. 3. ^ Om Vestindiena Pentacriner, loc. cit., p. 207. 

 * Systema Nuturw, ed. xii., Holmia', 1766, t. i. p. 1288. ^ Phil. Trans., 1865, p. 542. 



« Froc. Roy. Soc. Edin., vol. vii., 1872, p. 765 ; aud also The Depths of the Sea, p. 435. 



