BALL: MOLLUSCA AND BRACHIOPODA. 441 



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. 



TBLOTREMATA. 



Rhynchonellacea. 



Rhynchonellidae. 



HEITIITIIYRIS D'Orbigny. 



Hemithyris craneana Dall. 



Eemithyris craneana Dall, Proc. U. S. Nat. Mus., 1894, 17, p. 717, pi. 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 Dall, n. sp. 



Shell extremely thin and fragile, of a translucent very pale gray color, markedly 

 wider than high, smooth and polislied, 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 ctFect 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 heiglit 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 wliicli 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, glohigcr- 

 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 s|x>cies by its low beak, 

 wide trilobate form, and especially by having the median sulcus concave in the 



