OCR Text |
Show 514 PROF. F. J. BELL ON THE GENUS ASTERIAS. [May 3, occupied by short, frequently peg-shaped spines, which are generally set in transverse rows of three. Beyond and above this in the adult there are no indications of any rows of spines. The specimen from which the above description has been drawn up, and which is presumed to be adult, has R equal to 60, and r to 13 ; the arms are 15 millim. wide at the base, 4*5 near tip of arm; one arm has been lost. General coloration (after 40 years in spirit) light brown. Some much smaller specimens (22 = 23, z-=7*5 ; 22=18, r=8) from the same locality and collector, appear to belong to the same species: the development of the respiratory processes, though exceedingly well marked, has not attained to such an extraordinary pitch as in the more adult specimen; and, as a consequence, the tubercular spines on the abactinal surface and at the sides of the arm are more apparent. The processes, owing to some difference in refraction, and not because of the development of pigment, exhibit the most curious similarity to bivalved pedicellariae. Spaces bare of spines are found at the angles of the disk on the actinal surface. Two specimens rather larger (22 = 34, z*=9), which have a very close resemblance to the others in the number and arrangement of the adambulacral spines and the arrangement of the respiratory processes, differ from them in the well-marked development of rounded tubercle-like spines over the whole of the abactinal surface and in the absence of the bare space at the angle of the disk. They may for the present, at any rate, be regarded as varieties ; they are from the Falkland Islands also, but are of a rather deeper colour. ASTERIAS ROLLESTONI, n. sp. (Plate XLVIII. figs. 5, 5a.) General formula 2atc. Arms five, rather long, tapering gradually ; disk of moderate size adambulacral spines in a double row, those of the inner less numerous than those in the outer. Madreporic plate placed about halfway between the centre and the edge of the disk, anechinoplacid, very distinct, with a well-marked groove around it. The whole of the abactinal surface rough with irregularly disposed typacanthid spines, of which a rather obscure wavy line can be detected along the middle line of each ray. The adambulacral spines are stouter in the outer than in the inner row, but even there are not at all thick ; they are flattened, with broad, not pointed, free ends. The spines in the two rows beyond these are remarkably broad at their free end; and the character is more striking than in A. japonica of Stimpson ; they are thickly beset with pedicellariae. Two rows of much smaller spines are placed at the sides of the abactinal surface. The glistening white abactinal tubercles diminish somewhat in size from the centre of the disk towards the apex of the arms ; the respiratory processes are not collected into groups, but are distributed over the whole surface. 72 = 34, /• = 9*5. Breadth of arms at base 11 millim., near tip 2*5. Madreporic plate 3 millim. across. |