25.a—b). Further, the cups are as yet much less numerous than 
in the young of the typical form. This stronger development of 
the larger plates in the variety forms a very conspicuous character 
distinguishing the younger stages of the two forms. While in the 
variety they remain very distinet until a size of, at least 7—8 mm 
length, they are hardly discernible beyond the very youngest stages, 
2 —3 mm length, in the typical form. 
The young stages also give interesting information about the 
successive development of the various sorts of calcareous corpus- 
Fig. 25. Young specimens of Cueumaria 
brevideiitis,var.carnleyensis; a. from above; 
b. in side view. ^^/i. 
to draw apart from one another. 
cules. In the smallest specimens, 
1.5 mm long, of the variety the 
large plates alone are as yet 
developed. On the dorsal side 
' the cups have just begun to form 
over the edges of the larger plates. 
At a size of ca. 3 mm length 
the cups form a close layer in 
the skin, outside the large plates, 
but the buttons have not yet 
made their appearance. This latter 
sort of corpuscules, which is thus 
the last to develop, does not 
make its appearance until later, 
when, at a size of ca. 6—8 mm 
length, the larger plates begin 
so as to leave naked interspaces 
between them. In these interspaces the buttons are formed; it appears 
that no large plates are formed during the growth of the animal, the adult 
possessing only the same number of them as was found in the smallest 
young, and, consequently, while in the young specimens these large 
plates form a close mail, they lie widely scattered in the skin of 
the adult, discernible only as small spots, the skin being otherwise 
filled up with the small, knobbed buttons. — In the typical form, 
where the large plates do not form a close mail in the young stages 
the buttons begin to appear already at ca. 3—4 mm length. — 
Not rarely the large plates of the variety have a thickening at the 
overlapping point so as to be slightly spinous. Those around the 
anterior end are often somewhat prolonged so as to form valves 
