. Bulletin - United States National Museum. Science. Fig. r7.—Acasta spongites, EXMOUTH, TERGUM. Fig. 78.- -ACASTA JAPONICA, TERGUM OF TYPE. has an external depression or furrow to the spur. In A. spongites there is no furrow, but the flat spur-fasciol?* is bounded by lines. As there seems to be no figure of the exterior of the tergum of A. spongites I am illustrating it here for comparison with that of A. japonica, both figures being drawn to the same scale. The sculpture of the scutum is stronger in4. spongites, the longitudinal grooves more emphatic. In A. japonica the longitudinal sculptu

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. Bulletin - United States National Museum. Science. Fig. r7.—Acasta spongites, EXMOUTH, TERGUM. Fig. 78.- -ACASTA JAPONICA, TERGUM OF TYPE. has an external depression or furrow to the spur. In A. spongites there is no furrow, but the flat spur-fasciol?* is bounded by lines. As there seems to be no figure of the exterior of the tergum of A. spongites I am illustrating it here for comparison with that of A. japonica, both figures being drawn to the same scale. The sculpture of the scutum is stronger in4. spongites, the longitudinal grooves more emphatic. In A. japonica the longitudinal sculpture is of nar- row raised threads. Finally, the proportions of the valves are dif- ferent. In A. spongites the length of the tergum is but slightly more than three-fourths that of the scutum. In A. japo7iica it is seven- eighths. The breadth of the tergum is less than that of the scutum in .4. spongites, but in the Japanese species both valves have the same maximum breadth (fig. 78).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. United States National Museum; Smithsonian Institution; United States. Dept. of the Interior. Washington : Smithsonian Institution Press, [etc. ]; for sale by the Supt. of Docs. , U. S. Govt Print. Off.