ACANTIIOCHITKS. 23 



In astriger the pustules are very minute, crowded, and rounded, 

 each with a small central pit, as shown in fig. 56. The dorsal, areas 

 are wide, triangular and closely striated longitudinally. 



A. PYGM.EUS Pilsbry, P. sp. PI. 13, figs. 58, 59. 



Small, oblong, elevated, carinated, the side-slopes flat. Uniform 

 cream-white or olive-green, or variegated. 



Intermediate valves broad, somewhat beaked. Dorsal areas wide, 

 triangular, sculptured with longitudinal striae. Latero-pleural areas 

 evenly covered with rather large flattened pustules, which are 

 rounded or but slightly ovate, and average one-tenth of a mill, in 

 greatest diameter. Posterior valve having the tegmentum oval, wider 

 than long ; mucro prominent, subcentral. 



Interior blue or flesh-white. Posterior valve nearly semicircular 

 in outline behind, having a slit on each side, and a very slight 

 upward wave behind. The insertion-plate is short behind. 



Girdle narrow, having 9 small tufts of silver-white spicules on 

 each side, and an irregular fringe at the edge. 



Length 8, breadth 4 mill. ; divergence 100. 



Cedar Keys and Key West, Florida (Hemphill.) 



This is the smallest species of the genus known to me. It differs 

 from A. spieulosus in the smaller size, and high, roof-like form, in the 

 smaller tufts, comparatively much longer tegmenta, and in the shape 

 of the pustules, which are as coarse as in spieulosus, although the 

 shell is so much smaller. The posterior valve differs widely from 

 that of spieulosus. 



A. EXQUISITUS Pilsbry, n. sp. PI. 12, figs. 44, 45, 46, 47. 



Oblong, the visible portion of the valves very narrow, generally less 

 than one-fourth the entire width of the dried animal ; depressed. 

 Valves dark olive color; girdle of dried specimens light green, the 

 tufts very large and either green, pink or bronze colored. In well- 

 preserved alcoholic specimens the girdle is very fleshy and wide, 

 light yellow with green pubescence. 



The median valves are but slightly beaked, the tegmentum being 

 extremely narrow, its area far less than that of one of the sutural- 

 lamince. Dorsal area a rather narrow, longitudinally striated band, 

 wider in front. Side areas narrow, sculptured with separated, flat- 

 topped granules, round posteriorly, ovate or drop-shaped and con- 

 cave toward the anterior of each valve (fig. 47). Exposed portion 

 of anterior valve much shorter than the front slope of the insertion- 



