13 



are only two. There are two plates in the fourth range, except 

 in one area, where there are four, and two in the fifth range, to 

 which are united the points of the long pieces that lie between 

 the lobes on the dome, according to Lyon. Home specimens, how- 

 ever, we think show more than two plates, in the last range, in 

 some of the areas. 



There are from two to four intersecondary plates in each area 

 wedged between the arm bases; when four, tliey are in pairs, one 

 above the other. 



"The dome is covered by large pieces; each field between the 

 lobes contains a pair of the largest, which reach from the arm- 

 bases toward the proboscis; they are six or seven sided; long; 

 broadest at the upper extremity; pointed, or very slightly trun- 

 cated at the lower end; joining each other by their longest sides, 

 at the center of the depression between the lobes. A circle of 

 large pieces surround the dome; all of these rest partly upon the 

 ten long pieces. The pieces composing this zone are of different 

 sizes; they also differ in form; all six sided; two of the largest 

 pieces of the circle rest directly over two of the long pieces; three 

 other groups of the long pieces unite under the suture, uniting 

 two of the pieces forming the circle, so that the sutures, uniting 

 both sets of pieces, form one line from the arm bases to the base 

 of the second circle surrounding the dome near the base of the 

 proboscis. Below the zone described, and between the groups of 

 long pieces, are groups of from five to seven pieces, the upper 

 one of which is joined to the circle above the group of long 

 pieces, and on which it rests. The lowest piece of these groups 

 is lanceolate; is lodged between the arm bases, and unites with 

 the interbrachials. The upper and largest piece of these several 

 groups is of the same size and form as the pieces comprising the 

 first zone around the top of the dome. Around the arm bases the 

 pieces are numerous and quite small. The pieces comprising the 

 lower zone, and the large ones of the groups above the arms, are 

 surmounted by a group of from three to five rough, pointed spines, 

 confluent near their bases. The plates of the second zone at the 

 base of the proboscis are ornamented with hemispherical tubercles, 

 all other pieces of the dome are gibbous or concave and not orna- 

 mented." 



In this species there are from four to six pores between each 

 of the arm bases, that were not mentioned by Lyon, or shown in 



