DALL: MOLLUSCA AND BRACHIOPODA. vo Ae 
about 250 fathoms, of which two specimens were obtained, is a distinct species, 
which so far as we know does not reach the Magellanic region. 
THLOTREMATA. 
Rhynchonellacea. 
Ehynchonellidae. 
HEMITHYRIS D’Orsreny. 
Hemithyris craneana Datt. 
Hemithyris craneana Dall, Proc. U. S. Nat. Mus., 1894, 17, p. 717, pl. 31, figs. 5, 6. 
U.S. S. ‘‘ Albatross,” station 3362, off Cocos Island, Gulf of Panama, in 1175 
fathoms, mud, bottom temperature 36°.8 F. U.S. N. Mus. 122,861. 
A species of the general type of H. cornea Fischer, of the North Atlantic. 
Only one specimen was obtained. 
Hemithyris strebeli Datt, n. sp. 
Shell extremely thin and fragile, of a translucent very pale gray color, markedly 
wider than high, smooth and polished, except for occasional concentric lines due 
to resting stages; the surface under a lens shows a coarse prismatic structure, 
the imbricating ends of the prisms almost giving the effect of fine punctation ; 
beak low, sharp, small, with a wide delthyrium, widely triangular discrete del- 
tidial plates, and a small foramen, incomplete below; dorsal valve in the young 
flattish, in the adult deeply widely excavated mesially, with the anterior margin 
prominently extended into a correspondingly wide sinus in the margin of the 
ventral valve; ventral valve convex, in the adult almost trilobed with a broad, 
prominent mesial anterior convexity and corresponding marginal sulcus; interior 
of dorsal valve with a short, very low, thread-like septum about equal to one 
fourth the height of the valve; the hinge teeth close together, small, short, with- 
out props; muscular impressions obscure; crura short, blade-like, recurved, very 
easily detached ; ventral valve with no septum, the hinge teeth propped by plates 
between which and the valve are narrow recesses. Alt. 17; lat. 19; lat. of median 
sulcus, 11; max. diam. 9.5 mm. 
U.S. S. “ Albatross,” station 4721, in Mid Pacific, in 2084 fathoms, globiger- 
ina ooze, bottom temperature 35°.1 F. U.S. N. Mus. 110,741. Also at station 
4709, southwest of the Galapagos group, in 2035 fathoms, ooze, temperature 
35°.3 F. 
This shell is distinguishable from any other described species by its low beak, 
wide trilobate form, and especially by having the median sulcus concave in the 
