VIII DEVELOPMENT 239 
indications of five cephalic segments; the eyes, when present, 
are found at or near the front margin, and the free cheeks, if 
visible at all on the dorsal surface, are narrow. For this early 
larval form Beecher has proposed the name “ protaspis”; he 
regards it as the representative of the Nauplius of other 
Crustacea, but that view is not accepted by Professor J. S. 
Kingsley." 
The general changes which occur in the course of develop- 
mept are: modifications in the shape and relative size of the 
glabella, and of the number and depth of the glabella-furrows ; 
the growth of the free cheeks and the consequent inward move- 
ment of the facial sutures and eyes; the introduction of and 
gradual increase in number of the thoracic segments, and the 
relative decrease in size of the head. 
Sao hirsuta is a species found in the Cambrian, the develop- 
ment of which was fully described by Barrande. Its earliest 
protaspis stage (Fig. 143, A) is circular in outline; the glabella 
expands in front and c B A 
reaches the anterior 
margin; the pygidial > al 
region is not dis- e 0 ° 
tinctly separated 
from the cephalic 
region ; segmenta- 
tion 1s indicated in 
the former, and the 
neck-ring is present . 
in the latter; the 
: : Fic. 143.—Development of Sao hirsuta, Barr. Cambrian. 
eye-line 1s seen on A, Protaspis ; B-F, later stages; G, adult. The small 
each side of the outlines below each figure show the actual size of each 
specimen, (After Barrande. ) 
glabella near the 
anterior margin. Ina later stage (Fig. 143, C) the segmentation 
of the glabella becomes more distinct, indicating the existence of 
five cephalic segments, and the facial suture appears near the 
margin limiting a very narrow free cheek. Subsequently (Fig. 
143, D-F) the thoracic segments develop, and increase in 
number until the adult stage (G) is reached ; also the eyes appear 
at the margin of the cephalic shield, and gradually move inwards, 
and the glabella becomes narrower and rounded in front, and ceases 
1 American Geologist, xx., 1897, p. 34. 
