ECHINOIDEA. I. 89 



The tube feet have a typical sucking disk, as in an Echinus, but generally there are only 

 three leaves in the rosette (PI. VII. Fig. 10). In the mouth feet the sucking disk, as in an Echinus, is 

 an oval, continuous ring, of a far more complicate structure than the parts of the sucking disk in the 

 other tube feet The spicules (PL VII. Fig. 13) are small three-radiate, somewhat irregular bodies. In 

 the lower part of the tube feet almost none are found, nearest to the sucking disk they are more 

 numerous, and are here often a little branched and larger. No spicules are found in the skin at the 

 base of the spines, nor in the genital organs. 



The dental apparatus is of the structure common in the Echinoids; on the other hand the 

 auriculas are peculiar, only consisting of a pair of small processes, not joining above. None of the 

 specimens in hand show indication of any coloration. 



This little Echinid is especially interesting by nursing its brood a fact hitherto unknown 

 among the regular Echinids, with the exception of two Cidarids: Stereocidaris nutrix and canaliculata. 

 As mentioned in the description there are in $ a great many tubercles on the upper coronal plates, 

 and on the upper edge of the genital plates. The spines of these latter are bent downwards thus 

 joining those of the upper coronal plates. By this means a protected space is formed round the knob- 

 like process; the genital apertures open into this space, and here then the eggs and young are placed 

 protected by the spines (PI. VII. Fig. 5). The number of the eggs varies from 3 7; they are about 

 O'5 min in diameter. Sometimes they are all in the same stage of development, sometimes may be found 

 in the same individual almost quite developed young and eggs or embryos where the first skeletal 

 structures have not yet been formed. 



It was not possible, by means of the material in hand, to study the whole development of the 

 young, only a few stages have been given (PI. VII. Figs. 6 8). In the youngest stage (Fig. 6) the first 

 beginning of the teeth is seen; the buccal plates are begun, and the primary tentacles may be dis- 

 cerned through a plate, which I take to be the terminal plate (the ocular plate). Between each pair 

 of buccal plates, a little outside, a larger unpaired plate is found, the basal plate (the genital plate?). 

 In the following stage (Fig. 7) the different parts of the dental apparatus are begun , and in some of 

 the buccal plates a larger hole has appeared. In the oldest stage (Fig. 8), in each pair of buccal plates 

 one large opening has been formed for the buccal tube foot, and this feature of only one tube foot being 

 developed, is still found, as mentioned above, in young specimens of a diameter of 2 3 mm , and 

 sometimes in still larger specimens. The smallest individuals, in which I have found both buccal 

 tube feet developed, had a diameter of 4 mm . In the oldest stage figured, the five primary tube feet 

 are seen distinctly, and the five first spines, interambulacral ones, are begun. In corresponding stages 

 only one large anal plate is found (PI. VII. Fig. 14), which may be perforated by a larger opening; 

 accordingly it seems quite to encompass the anal aperture. 



Of this especially interesting little Echinid several specimens have been taken by the Ingolf*- 

 Expedition on the following stations: 



St. 73 (62 58' N. Lat. 2328'W. L. 486 fathoms. 5 i bottom temp. Bottom [?]). i specimen. 



-78 (60 37' 27 52' 799 4 i Mud. " ). 40 



- 81 (6i44' 27 1 1' 485 5 7 ). 18 



- 84 (62' 58' 25 24' 633 4 4 ). 15 



The Ingolf-Expedition. IV. i. IZ 



