Obliquely oval, inflated, solid, whitish with thin periostracum in radial rows, with fine radial ribs crossed by commarginal ridges forming beads, no byssal gape; interior whitish, margin denticulate, cardinal area narrow, hinge line straight, with <12 teeth. North Carolina, Florida Keys, West Indies, Gulf of Mexico. Length 6 mm.

Shell similar in general shape, size, and sculpture to A. pectunculoides, but shorter and higher, with a perfectly different hinge, and bearing much the same relation to that species that Limopsis minuta does to L. aurita. The ex¬ternal concentric sculpture is the most enduring, and is always preserved, while the radiating sculpture, sometimes strong, is often evanescent ; the radiating sculpture always appears inside the shell within the margin (which is smooth and polished) in a series of small ridges, generally with the same level as the rest of the interior, but sometimes rising into little tubercles, and separated by rather deep, short, narrow depressions, which do not extend far inward nor over the smooth margin; hinge straight, with from fifteen to seventeen stout nearly vertical teeth, usually in a continuous series ; an occasional specimen shows a gap in the middle through the atrophy of one of the small central teeth ; those at the ends of the series are oblique, as usual, but the series itself forms a straight line. In A. pectunculoides, on the contrary, all the teeth are oblique and very much more slender ; there are usually only five or six at each extremity of the hinge-line, and the middle part is either quite edentulous or only lightly irregularly granulous. A. glomerula measures as follows : lon. 5.75 ; alt. 5.0; diam. 5.0 ; lon. of hinge-line, 4.25 mm. A specimen of A. pectunculoides measures: lon. 7.75 ; alt. 7.5; diam. 5.5 ; lon. of hinge-line, 6.25 mm.
Barbados, 100 fins.; Bache, April 22, 1872, lat. 21° 14', 100 fms.; Station 20, 220 fms.; Station 19, 310 fms.; Sigsbee, off Havana, 450-480 fms.
Considering the great variability of abyssal shells it is possible this may eventually rank only as a variety of A. pectunculoides, but with the material at hand I cannot see the way clear to unite them at present.

Addition:
The specimens described by me in 1881 were separated valves, and the differences of sculpture, noted at the time, were set down to individual variation. Mr. Smith has, however, shown that the difference is between the two valves of the same specimen. There is generally a single more prominent rib on the posterior slope of the right valve, but nothing of the kind in the left valve. Habitat. Barbados, 100 fms.; Bache, April 22, 1872, Lat. 21° 14', 100 fms.; Station 20, 220 fms.; Station 19, 310 fms.; Sigsbee, off Havana, 450-480 fms.; Station 100, off Havana, in 400 fms.; Stations 206 and 211, in 170 and 357 fms. off Martinique, bottom temperature 49°.0 F. to 62°.0 F. The Challenger specimens were obtained from off Culebra Island, West Indies, at Station 24, in 390 fms., pteropod ooze.