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2 mm. Color of the body is light brown. The 
rather swollen prothorax (Fig. 9) measures 
about a third of the entire length. The rounded 
buccal plate is pierced by the mouth opening. 
The spicules (Fig. 10), including the small 
ones, are distinguished by a distinct keel; the 
pointed thornlike spicules of the hind end bear 
conspicuous brown incrustations. With the ex- 
ception of the gill retractors, the muscles are 
fairly weak; the longitudinal ones split up into 
five or six bundles on each side before giving 
origin to two pairs of dorsal and three pairs 
of lateral retractors of the front end. Among 
the usual six pairs of gill retractors, the dorsal 
posterior ones are markedly thick and partly 
attached to the wall of the cloacal chamber 
between the two gills. The posterior vertical 
FIG. 9- Crystallophrisson reel sum. Entire animal in 
side view, showing the body regions, a, h, c, d. from 
which are taken the spines named in the text. 
FIG. 10. Crystallophrisson recisum. Spines from 
body regions, showing characteristic ones from regions 
a, b, c, and d. (Compare with Fig. 9.) 
diaphragm is very strong. Three free gill- 
lamellae on each side arise from the cloacal 
wall. The nervous system is typical; the location 
of the brain is rather far back above the radula. 
The cerebro-buccal connective is split off the 
common trunk shortly behind its origin. The 
narrow fore-gut possesses a very strong sphinc- 
ter some distance from the mouth opening; 
buccal glands are to be found only in front 
of it. The three kinds of salivary glands are 
present but are unusually small; the radula is 
