204 
THE CORAL TRIANGLE: HEARST BIODIVERSITY EXPEDITION 
Figure 26. Acasta vipensis, opercular plates ofparatype, CASIZ 185883. A scutum exterior; B scutum interior; C ter- 
gum exterior; D tergum interior. Scale bar = 200pm. 
Description. — Shell conical with short calcareous spines protruding from parietes, radii 
broad and disparietal, orifice with jagged summits, orifice sloping from carina to rostrum. Carina 
highest wall plate, carino-latera next highest, then latera, with rostmm about one half height of cari¬ 
na. Basis flat, oval, with shallow grooves aligned with the six wall plate sutures. Scutum exterior 
with latticed appearance due to longitudinal ridges crossing growth ridges; apex acute; adductor 
and depressor muscle pits shallow to not visible; articular ridge convex, approximately ^2 length of 
scutum; basal margin broadly convex, tergal and occludent margins fairly straight; interior smooth. 
Tergum with short tmncated spur, rounded point on basal margin of spur near articular margin; 
apex mildly beaked; depressor crests very faint or not present; scutal margin concave; carinal mar¬ 
gin convex; interior smooth; articular ridge mild, concave; basicutal angle moderate to shallow, 
wide. Labrum with deep narrow notch, 2-4 teeth either side of notch. Mandible with 5 teeth, 1 
and 2^^ slightly farther apart than 2nd and S^d; 2nd and S^d teeth may be bifurcated; 4^^ and 5^^ teeth 
clumped together near inferior angle; inferior and superior margins with long fine setae, shorter 
setae along cutting edge. Maxilla cutting edge with 8-9 large spines; last large spine may or may 
