“Lonchotaster tartareus, n. sp. (Pl. XVI. figs. 1-5).
Rays five. In the largest specimen R = 88 + mm., r 20.5 mm. Breadth of the ray at the sixth supero-marginal plate, 16 mm. (The tip is wanting in all the rays of this example.) In a smaller but perfect example R = 55 mm., r = 14 mm. Breadth of the ray at the sixth supero-marginal plate, 9.5 mm.
Rays moderately elongate and comparatively narrow, tapering gradually to a pointed extremity, the outer part of the ray being attenuate and subcylindrical. Interbrachial arcs wide, open, and well rounded. Abactinal area convex and more or less inflated. Actinal area plane. Lateral walls low, very slightly rounded. In all the specimens collected the rays are sharply turned back over the disk, nearly from their base.
The abactinal area of the disk and rays is covered with numerous small and closely packed paxillae; these are composed of ten to fifteen small, erect, cylindrical, obtusely rounded, skin-covered papillae, three to five being central. In a very large number of the paxillae two to four of the central papilla are enlarged and form a pedicellarian apparatus. In consequence of their skin investiture and erect position the separate papillae are not noticeable to the naked eye, only the paxillae as a whole being distinguished; the paxillar area in consequence has a smooth and highly compact appearance. The paxillae present no definite order of arrangement.
The marginal plates are small and confined entirely to the lateral wall of the ray. The supero-marginal plates are forty-five in number counting from the median interradial line of the longest remaining ray, from which, however, the tip has been broken in the large specimen, with an estimated loss of twenty to thirty plates. Fifty-three are present from the median interradial line to the extremity in a smaller example in which R = 55 mm. The plates are rectangular, with the height rather greater than the length on the inner part of the ray, but subequal on the outer part; and only the upper edge of the plate is visible on the abactinal surface. The plates are covered with low granule-like papillae, often somewhat squamiform, but longer, more delicate, and cilia-like along the lateral sutures. The supero-marginal plates are devoid of any true spines, but within the interbrachial arc and at the base of the rays in the large example, a small conical tubercle is present close to the upper end of the plate, but it is not found in the smaller specimens. On some of the plates three or four of the papillae are slightly enlarged and form an incipient pedicellarian apparatus, the position of which is usually near the aboral margin and not far from the junction of the supero-marginal and infero-marginal series.
The infero-marginal plates correspond exactly in length to the superior series, but their height is distinctly greater, appearing near the middle of the ray nearly twice as great as that of the superior series. Within the interbrachial arc they form a broad border to the actinal area of the disk, but this extent on the actinal area speedily diminishes along the ray, where they are confined essentially to the lateral wall, and their curvature only conforms to the rotundity of the ray. Their surface is covered with papillae similar to those on the superior series. At the upper margin of normally every infero-marginal plate, and close to the junction with the superior series, is a conspicuous pedicellaria, formed of three or four enlarged and modified papillae; the apparatus being larger and more fully developed than those on the supero-marginal plates above noticed ; sometimes two are present on one plate. In the interbrachial arc about a dozen plates may bear a single small, flattened, tapering, pointed spinelet immediately behind the pedicellaria, but so small that it is little more than an enlarged squamule.
The adambulacral plates are large and missive, rather longer than broad, and with a slightly convex margin towards the furrow. Their armature consists of a furrow series of nine or ten rather short, robust, subprismatic, skin-covered spinelets, equal in length, excepting the outermost at each extremity, and standing parallel to one another and erect, forming a nearly straight series. Each successive series is well-defined. On the actinal surface of the plate, behind the furrow series, is a longitudinal series of about seven shorter spinelets, well-spaced, covered with membrane, which gives them a more or less strongly fusiform appearance; and behind these again two or even three series of small papilliform, skin-covered spinelets, in which the longitudinal arrangement is often more or less disturbed and irregular in consequence of additional papillae; the outer part of the plate being well filled. At the aboral end of the line of the second aeries of spinelets on the actinal surface is one large pedicellaria, formed of three or four large modified papillae; this apparatus is present on every plate, and forms a conspicuous object.
The mouth-plates are large, elongate, prominent, and convex actinally. The outline of the united pair somewhat resembles that of a classical spear-head, in consequence of an angle at the junction of the free margin with the margin adjacent to the first true adambulacral plate. Their armature consists of a marginal series of twelve to fifteen short, erect, skin-covered spinelets on each plate, similar to, but smaller than, those on the adambulacral plates, which are nearly subequal in length, or increase very slightly as they proceed inwards. The actinal surface of the plates is covered with numerous small, low, skin-covered papillae, which increase in size on the inner part of the plates, but become quite small and granuliform on the outer part, especially towards the margin opposite to the median suture. Though numerous these papillae are distinctly spaced, but no order of arrangement is distinguishable.
The actinal interradial areas are email, and confined to the interbrachial region, not appearing to extend beyond the fifth or sixth infero-marginal plate counting from the median interradial line; they are occupied by small intermediate plates arranged in regular columns, which bear a number of small, short, skin-covered papillae, with three or four much larger than the rest in the midst, forming a massive pedicellarian apparatus; a few of the innermost plates in the large specimen have one papilla more spiniform than the others, and this may either be present along with the pedicellaria or in its place.
The anal aperture is subcentral and distinct, although there is no change in the form of the paxillae in its neighbourhood.
The madreporiform body is compound, and occupies a large circular area about 10 mm. in diameter, its outer edge being not more than 2 or 3 mm. distant from the marginal plates. Numerous large paxillae, much greater than any of the others on the abactinal area, spring from, or at the junction of, the madreporic plates, almost entirely hiding the striated surface from superficial view. This may be seen in places, however, for the paxillae are not very closely placed, and here and there one is wanting. The striations are seen to be very fine, numerous, and very slightly convoluted. The papillae which compose these paxillae are rather more robust and distinct than those of the general paxillae, having more the appearance of hemispherical granules when seen from above; and none are modified into pedicellariae.
Colour in alcohol, a bleached yellowish white. On one of the small specimens there are traces of a dark purple colour along one of the rays, but whether this is the original colour of the species, or is only pigment derived by abrasion from some other organism, I am unable to say.
Locality.—Station 89. Between the Canaries and the Cape Verde Islands. July 23, 1873. Lat. 22° 18' 0" N., long. 22° 2' 0" W. Depth 2400 fathoms. Globigerina ooze. Bottom temperature 36.6° Fahr.; surface temperature 73.5°5.”
(Sladen, 1889: 104-106)
