| OCR Text |
Show 377 its other slightly- sloping npper side, first by two large plates in direct succession, the npper one of which is larger than the other, wider than long, generally hexagonal in form, and gives off on the interaxillary side another arm- like series of pieces, which pieces diminish rapidly in size upward, and connect with a corresponding series from the other division of the ray over the interaxillary space, so as to isolate the interaxillary pieces. At least, a few of the lower pieces of these little armlike series over the interaxillary spaces are fastened together and to the adjacent parts, to form portions of the walls of the body. The next piece of the main division of each ray, above that last mentioned, also gives off, on the interradial side, another arm- like series of pieces, some of the lower of which are fastened to those of the larger series first described. Above this, the main divisions of the rays soon become free arms, composed of much shorter, transversely- oblong; or slightly wedge- shaped pieces, apparently every second one of which gives off alternately, on opposite sides, short, free pinnules. Soon the arms become rounded, on the outer or dorsal side, with a deep ambnlacral furrow within; while beyond they very gradually taper and extend to great lengths, apparently without bifurcating. In all cases, they and the intermediate arm- like divisions draw together rapidly at the upper part of the body before becoming free, and thus seem to reduce the vault or ventral area to comparatively small dimensions. The specimen represented by Fig. B shows one of the interradial areas ( or possibly it may be the anal) to be rather large, and occupied by nine unequal plates, the lower one of which is wider than high, hexagonal in form, and supports two nearly as large heptagonal pieces in the next range, while those above are of various forms and sizes, and more or less irregularly arranged. Mr. GrinnelPs Fig. 1 also shows about the same number of pieces in one of these areas, but they are somewhat differently arranged. Of ' the interaxillary spaces, our specimens show only two in one specimen, and one in another, and each of these is occupied by only two interaxillary pieces, generally of heptagonal form, and placed directly one above the other. In order that the interradial and interaxillary series of plates may be the more readily distinguished from those belonging to the radial system, I have had a light shade drawn over the former in figure B, and a dotted line run up each of the rays and its subdivisions. None of our specimens retain the arms much above the summit of the body; but Mr. Grinnell says that in some of those studied by him they can be traced to a length of eight inches, and yet have the ends broken off, so that he thinks they may have attained a length of not less than one foot. One of his figured specimens shows a large number of long, slender, jointed pieces that seem to be portions of slender, detached, simple arms, bearing short pinnules, apparently in some cases springing one from each joint. As much as the small interradial arm- like divisions of the rays look like a series of smaller arms springing from the summit of the interradial pieces, it is evident that they are really parts of the radial system, or, in other words, divisions given off from the secondary radials; and the same may be said of those seen in the interaxillary spaces. In fact, they all correspond to the pinnules of the free rays or arms in all respects, excepting that they are larger, and united with each other and with the main divisions of the rays for some distance up, so as to constitute a part of the walls of the body. Some of the characters mentioned in these remarks are generic and some merely specific, as we have not yet the means of giving separate generic and specific diagnoses from such specimens as have been found. |
